'git commit' and 'git tag -a' enforce some conventions, like cleaning up excess whitespace and making sure that the last line ends with a '\n'. This fix replicates this behavior.

Fix libgit2/libgit2sharp#117

git_commit_create is supposed to update the given reference
"update_ref", but segfaulted in case of a yet to be born
reference. Fix it.

Signed-off-by: schu <schu-github@schulog.org>

Signed-off-by: schu <schu-github@schulog.org>

There's no difference between `_free` and `_close` semantics: keep
everything with the same name to avoid confusions.

There were quite a few places were spaces were being used instead of
tabs. Try to catch them all. This should hopefully not break anything.
Except for `git blame`. Oh well.

1. The license header is technically not valid if it doesn't have a
copyright signature.

2. The COPYING file has been updated with the different licenses used in
the project.

3. The full GPLv2 header in each file annoys me.

A bunch of redundant methods have been removed from the external API.

- All the reference/tag creation methods with `_f` are gone. The force
flag is now passed as an argument to the normal create methods.

- All the different commit creation methods are gone; commit creation
now always requires a `git_commit` pointer for parents and a `git_tree`
pointer for tree, to ensure that corrupted commits cannot be generated.

- All the different tag creation methods are gone; tag creation now
always requires a `git_object` pointer to ensure that tags are not
created to inexisting objects.