Implement hesokuri.git/remove-entry

This is used in a manner similar to add-blob, in that it transforms a tree that
can be written back to the repo with write-tree.

Ultimately, this will be used when the user must modify the configuration, which
will soon be stored in a database (see the namespace docstring of
hesokuri.hesobase)
Merge branch 'origin-master'

Conflicts:
	test/hesokuri/git_test.clj
Fix formatting in hesokuri.git/remove-entry

- Use , to indent the last continued 'cond' entry. Considered doing this for the
  hesokuri.git/remove-entry test case, but this made the code look more
  cluttered. Decided using blank lines is more natural for this case.
- Do not use arity-overloading syntax for the defn, since there is only one
  arity for this function.
Merge pull request #12 from matvore/master

Implement hesokuri.git/remove-entry