git: Refactor class and method descriptions.
test_git: Fix the order of imports.
git: Add a new class: Commit.
git: Add a new class: Branch.
test_git: Refactor CommitTests.
git: Validate the length of a hash.
git: Validate the characters appearing in a hash.
git: Refactor the magic literals 40 and 'abcdef0123456789' into class constants.
test_git: Refactor get_rand_hash() and use it in more tests.
git: Add commit hash normalization.
test_git: Refactor the creation of the today's date.
test_git: Fix get_curr_date() to return also the number of seconds.
test_git: Rename CommitTests to CommitCreateTests.
git: Add __eq__() and __ne__() to Commit.
test_git: Use a full import for datetime.
git: Add Commit.__repr__().
git: Wrap a long line in the description of Git.
test_git: Fix test_hash_is_properly_normalized().
test_git: Wrap long lines.