minor: remove trailing whitespace
Add smarter remote/repo detection via Git's upstream remote

 - Add a new option `g:github_issues_default_remote` (default "origin"),
   which is used as a fallback if no upstream remote is configured.

I have left two print statements to get notified about what
vim-github-issues is doing for now.

Fixes #107.
Cleanup "Remove trailing ".git" segment from path"
getRepoURI: also cache empty repos / lookup failures
Merge branch 'improve-upstream-remote' of https://github.com/blueyed/github-issues.vim into blueyed-improve-upstream-remote

Conflicts:
	plugin/githubissues.vim
Remove debug statements
Merge branch 'master' of github.com:jaxbot/github-issues.vim