Sets the current head to the specified commit oid and optionally resets the index and working tree to match.
SOFT reset means the Head will be moved to the commit.
MIXED reset will trigger a SOFT reset, plus the index will be replaced with the content of the commit tree.
HARD reset will trigger a MIXED reset and the working directory will be replaced with the content of the index. (Untracked and ignored files will be left alone, however.)
TODO: Implement remaining kinds of resets.
Committish to which the Head should be moved to. This object must belong to the given repo
and can either be a git_commit or a git_tag. When a git_tag is being passed, it should be dereferencable to a git_commit which oid will be used as the target of the branch.
0 on success or an error code