Includes trial documentation for git-freeze and git-thaw, as well as a
make_docs.sh script which generates man and html documentation from the input
asciidoc files, using git 1.9's documentation toolchain.

R=szager@chromium.org, agable@chromium.org
BUG=261738

Review URL: https://codereview.chromium.org/196133007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@257214 0039d316-1c4b-4281-b951-d872f2087c98