:lipstick: test code
introduced test helper for creating repository data
added test to ensure you can change the targetcommitish field
Merge branch 'master' into releases-can-should-change-commitish
Merge pull request #536 from octokit/releases-can-should-change-commitish

releases can/should change commitish
Trivial fixes in XML comments

And added an #if around using in RequestParameters.cs (worth having a
look, may have implications when building on different platforms)
Merge pull request #538 from vcaraulean/code-doc-fixes

Trivial fixes in XML comments