Add branch querying/filtering feature

The git-branch doc states

With --contains, shows only the branches that contain the named commit (in other
words, the branches whose tip commits are descendants of the named commit).

With --merged, only branches merged into the named commit (i.e. the branches whose
tip commits are reachable from the named commit) will be listed.

With --no-merged only branches not merged into the named commit will be listed.

If the <commit> argument is missing it defaults to HEAD (i.e. the tip of the
current branch).

A potential API design might rely on the following

• Add a QueryBy() method to the BranchCollection in a similar way to the CommitCollection.QueryBy() method.
• Rename the current Filter type to CommitFilter, in order to allow the creation of a BranchFIlter

Binding the following method might also be helpful. Related libgit2 tests can be found here.

/**
 * Find a merge base between two commits
 *
 * @param out the OID of a merge base between 'one' and 'two'
 * @param repo the repository where the commits exist
 * @param one one of the commits
 * @param two the other commit
 */
GIT_EXTERN(int) git_merge_base(
     git_oid *out,
     git_repository *repo,
     git_oid *one,
     git_oid *two);

Inizia con BranchCollection e confronta la sua API QueryBy() proposta con CommitCollection.QueryBy(). Esamina il tipo Filter attuale prima di prendere in considerazione la ridenominazione proposta, quindi ispeziona i test di revwalk/mergebase.c di libgit2 e il binding git_merge_base. Il lavoro è completo quando le query branch contains/merged/not-merged e la relativa API merge-base sono definite con test corrispondenti e il design dell’API è stato stabilito.