Enumerate refspecs

The Remote.RefSpecs property allows to enumerate over all refspecs defined for a specific remote.
Update libgit2 binaries to 98eaf39

https://github.com/libgit2/libgit2/compare/e87d9d3...98eaf39
First stab at blame marshalling
Spike Repository.Blame
Fix marshalling structures
Avoid stealing ownership of signatures
Hunk by-line accessors
Another marshalling test
Don't use nested classes
Satisfy MetaFixture
Dispose of native blame handle asap
Newlines at end of new files
Expose Blame on IRepository
Move blame flag mapping to extension method
Use LaxUtf8Marshaler
BlameStrategy.Normal -> Default
Ifs should have braces
Move blame options to external class
Use CLS-compliant types
Don't keep pointers to native blame hunks