Replace unreliable (featurep 'color) check in rainbow-mode package guard

See #91
Add a binding for vc-git-grep
Use haskell-mode for .ghci files
Add bug-reference-github, and keep github-related config together
Use switch-window package for improved "C-x o" support
Remove binding of C-` for flymake-goto-next-error
Check emacs version within eval-when-compile
Enable delete-selection-mode explicitly, though cua-mode already enables it
Correct note about running prog-mode-hook for ruby-mode
Merge remote-tracking branch 'upstream/master'