Merge pull request #103 from kciccarello/master

Changed v0.18.0.json so diffWorkDir DiffOptions argument is optional. Ad...
Duplicate git_error before passing it on as it will cross a thread boundary.
Regenerated sources.
Merge pull request #106 from kciccarello/master

Updated v0.18.0.json to make the index and DiffOptions arguments in Inde...
Checking for nulls; freeing memory
Merge branch 'master' of github.com:nodegit/nodegit