convert documentation files to markdown

* format section headings, links and code snippets
* add .md file extension to trigger pretty rendering on Github
* standardize on lowercase typesetting for git-crypt

INSTALL.md

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+Dependencies
+------------
+
+To use git-crypt, you need:
+
+*   Git 1.6.0 or newer
+*   OpenSSL
+*   For decrypted git diff output, Git 1.6.1 or newer
+*   For decrypted git blame output, Git 1.7.2 or newer
+
+To build git-crypt, you need a C++ compiler and OpenSSL development
+headers.
+
+
+Building GIT-CRYPT
+------------------
+
+The Makefile is tailored for g++, but should work with other compilers.
+
+    make
+    cp git-crypt /usr/local/bin/
+
+It doesn't matter where you install the git-crypt binary - choose wherever
+is most convenient for you.
+
+
+BUILDING A DEBIAN PACKAGE
+
+Debian packaging can be found in the 'debian' branch of the project
+Git repository.  The package is built using git-buildpackage as follows:
+
+	$ git checkout debian
+	$ git-buildpackage -uc -us
+
+
+INSTALLING ON MAC OS X
+
+Using the brew package manager, simply run:
+
+        $ brew install git-crypt

NEWS.md

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+News
+====
+
+######v0.3 (2013-04-05)
+*   Fix 'git-crypt init' on newer versions of Git.  Previously,
+    encrypted files were not being automatically decrypted after
+    running 'git-crypt init' with recent versions of Git.
+*   Allow 'git-crypt init' to be run even if the working tree contains
+    untracked files.
+*   'git-crypt init' now properly escapes arguments to the filter
+    commands it configures, allowing both the path to git-crypt and the
+    path to the key file to contain arbitrary characters such as spaces.
+
+######v0.2 (2013-01-25)
+*   Numerous improvements to 'git-crypt init' usability.
+*   Fix gitattributes example in README: the old example showed a colon
+    after the filename where there shouldn't be one.
+*   Various build fixes and improvements.
+
+######v0.1 (2012-11-29)
+*   Initial release.

README.md

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+GIT-CRYPT
+=========
+
+git-crypt enables transparent encryption and decryption of files in a
+git repository.  Files which you choose to protect are encrypted when
+committed, and decrypted when checked out.  git-crypt lets you freely
+share a repository containing a mix of public and private content.
+git-crypt gracefully degrades, so developers without the secret key can
+still clone and commit to a repository with encrypted files.  This lets
+you store your secret material (such as keys or passwords) in the same
+repository as your code, without requiring you to lock down your entire
+repository.
+
+git-crypt was written by Andrew Ayer <agwa at andrewayer dot name>.
+For more information, see <http://www.agwa.name/projects/git-crypt>.
+
+
+Building git-crypt
+------------------
+See the INSTALL file.
+
+
+Using git-crypt
+---------------
+
+Generate a secret key:
+
+    git-crypt keygen /path/to/keyfile
+
+Configure a repository to use encryption:
+
+    cd repo
+    git-crypt init /path/to/keyfile
+
+Specify files to encrypt by creating a .gitattributes file:
+
+    secretfile filter=git-crypt diff=git-crypt
+    *.key filter=git-crypt diff=git-crypt
+
+Like a .gitignore file, it can match wildcards and should be checked
+into the repository.  Make sure you don't accidentally encrypt the
+.gitattributes file itself!
+
+Cloning a repository with encrypted files:
+
+    git clone /path/to/repo
+    cd repo
+    git-crypt init /path/to/keyfile
+
+That's all you need to do - after running `git-crypt init`, you can use
+git normally - encryption and decryption happen transparently.
+
+
+Current Status
+--------------
+
+The latest version of git-crypt is 0.3, released on 2013-04-05.
+git-crypt aims to be bug-free and reliable, meaning it shouldn't
+crash, malfunction, or expose your confidential data.  However,
+it has not yet reached maturity, meaning it is not as documented,
+featureful, or easy-to-use as it should be.  Additionally, there may be
+backwards-incompatible changes introduced before version 1.0.
+
+Development on git-crypt is currently focused on improving the user
+experience, especially around setting up repositories.  There are also
+plans to add additional key management schemes, such as passphrase-derived
+keys and keys encrypted with PGP.
+
+
+Security
+--------
+
+git-crypt is more secure that other transparent git encryption systems.
+git-crypt encrypts files using AES-256 in CTR mode with a synthetic IV
+derived from the SHA-1 HMAC of the file.  This is provably semantically
+secure under deterministic chosen-plaintext attack.  That means that
+although the encryption is deterministic (which is required so git can
+distinguish when a file has and hasn't changed), it leaks no information
+beyond whether two files are identical or not.  Other proposals for
+transparent git encryption use ECB or CBC with a fixed IV.  These systems
+are not semantically secure and leak information.
+
+The AES key is stored unencrypted on disk.  The user is responsible for
+protecting it and ensuring it's safely distributed only to authorized
+people.  A future version of git-crypt may support encrypting the key
+with a passphrase.
+
+
+Limitations
+-----------
+
+git-crypt is not designed to encrypt an entire repository.  Not only does
+that defeat the aim of git-crypt, which is the ability to selectively
+encrypt files and share the repository with less-trusted developers, there
+are probably better, more efficient ways to encrypt an entire repository,
+such as by storing it on an encrypted filesystem.  Also note that
+git-crypt is somewhat of an abuse of git's smudge, clean, and textconv
+features.  Junio Hamano, git's maintainer, has said not to do this
+<http://thread.gmane.org/gmane.comp.version-control.git/113124/focus=113221>,
+though his main objection ("making a pair of similar 'smudged' contents
+totally dissimilar in their 'clean' counterparts.") does not apply here
+since git-crypt uses deterministic encryption.
+
+git-crypt does not itself provide any authentication.  It assumes that
+either the master copy of your repository is stored securely, or that
+you are using git's existing facilities to ensure integrity (signed tags,
+remembering commit hashes, etc.).
+
+
+MAILING LISTS
+
+To stay abreast of, and provide input to, git-crypt development, consider
+subscribing to one or both of our mailing lists:
+
+Announcements: http://lists.cloudmutt.com/mailman/listinfo/git-crypt-announce
+Discussion:    http://lists.cloudmutt.com/mailman/listinfo/git-crypt-discuss