branch: Implemented branch functions.
branch: Changed BranchT to BranchType
branch: Variable names don't repeat its type name any longer
branch: Renamed BranchCreate to CreateBranch
branch: Renamed BranchLookup to LookupBrnach
branch:BranchForeach: Correct handling of the ListFlags
branch: Deleted BranchForeach
Add a few reference utility functions
Allow for a default in reflog messages

We don't have a way to represent a NULL string, so if the user passes an
empty string, let's pass NULL down so we tell libgit2 to use the default.
Merge branch 'branch_functions' of http://github.com/JohannWeging/git2go into merge-add-branch-lookup
cleanup add-branch
Add thread locking
Merge branch 'master' of https://github.com/libgit2/git2go into add-branch-lookup
LastError -> MakeGitError
Merge pull request #60 from libgit2/cmn/reflogs-default

Allow for a default in reflog messages
Merge pull request #59 from libgit2/cmn/refs

Add a few reference utility functions
Fix an old error function call that snuck in
Add a travis script

Add a build script and ask Travis to run it. It downloads the tip of
libgit2's dev branch and tests against that.
fix bad git_buf handling
Remove unused consts