MakeMaker.pm: Search for libssh2 includes and libs in /usr/local
Raw.xs: import ppport.h
travis: install libssl and libssh2 as well
travis: run release tests too
MakeMaker.pm: (try to) support building libgit2 on windows
MakeMaker.pm: remove TODO
MakeMaker.pm: fix access to %os_specific hash
Walker.xs: properly create Commit objects in next() (closes #52)
Changes: update
add modifications suggested by ppport.h
Raw.xs: more ppport
v0.31

 - Fix include paths on FreeBSD (GH#49) (GH#50) (thanks, @jacquesg!)
 - (Try to) support building libgit2 on Windows
 - Properly create Commit objects in Walker -> next()
   (GH#52) (thanks, @karel-m for the test case!)
Update to libgit2 494be42
Fix interface changes due to libgit2 upgrade

* Most repository changing functions now need a signature
* Duplication functions i.e. git_signature_dup now return an error code
* libgit2's merge API has renamed some constants/options/flags
travis: install Pod::Coverage::TrustPod as well
MakeMaker.pm: fix regex include path on Win32
Changes: update