Drop obsolete members after release v0.14.1
Cleanup temporary test repos before each test run
Cleanup FilterBranchFixture test repositories
Update libgit2 binaries to 711333e

https://github.com/libgit2/libgit2/compare/11f8336...711333e
Ensure shadow copying doesn't prevent from probing
Introduce RequiresDotNetOrMonoGreaterThanOrEqualTo() helper
Make RetrieveStatus() reload on-disk index beforehand

Fix #322 and #522
Enforce creation of unborn branch test coverage
Protect Signature creation from components containing '\0'
Protect Signature creation from invalid parameters
Protect Commit creation from message containing '\0'
Protect TagAnnotation creation from name or message containing '\0'
Protect TagAnnotation creation from invalid parameters
Refactor Marshalers
Split Patch and TreeChanges generation

Remove Patch from TreeChanges
Make repo.Diff.Compare() generic
Introduce EncodingMarshaler.Cleanup()
Make string marshaling either lax or strict
Enforce repo.Network.Push()  test coverage
Allow push APIs to set packbuilder parallelism
Introduce blob FilteringOptions for content stream

Get the content of a blob as it would be checked out to the
working directory via the filters.