add test for segfaults in revwalk
change the way classes free themselves
change "createX" methods to "create"

also blocks instantiation of types from JS
fix linting
expose gc for travis
move to nannew for boolean passing of selfFreeing
fix issue with building in v11 using nanreturnvalue
add custom macro for dealing with returning while escaping a scope in js methods
Merge pull request #250 from nodegit/refactor-classes

Refactor classes
Added more git_cred methods