Add `prelude-github`

Conflicts:
	core/prelude-core.el
Use move-text to allow moving up or down of the selected region as well
[Fix #365] Don't indent with tabs in c-mode
[Fix #391] Ask for confirmation before deleting a file that's not under VC
Enable smartparens-strict-mode in Lisps
Add a few extra Magit keybindings
Merge branch 'master' of https://github.com/bbatsov/prelude