- Create BranchProtection models
- Add Protection element to Branch model
- Adjust RepositoryClient GetBranch and GetBranches calls to set the special preview accepts header to enable Protected Branches API (currently in preview)
- Adjust tests to include preview accepts header
- Add test for Protection element
It's bothered me that our response models are mutable. They really
shouldn't be. I made the properties have a protected setter instead of
private to provide flexibility for others who might be deriving from
these classes or testing them.
Fixes#650