Update BranchesService Methods. (#156)
Update BranchesService Methods. (#156)

This change breaks backwards compatibility.

The BranchesService methods were almost all inconsistent with other Services and not supplying all available options. Also updated all documentation links.

The Branch struct now includes all properties exported by the v3 API.
ListBranches takes a new ListBranchesOptions struct for pagination.
Added the ability to configure the branch protection in line with API documentation.
Added a new DeleteMergedBranches which is part of the branches page.
samuelthomps0n/go-gitlab,xanzy/go-gitlab,nyxi/go-gitlab,mickymiek/go-gitlab