[Fix #426] Remove M-O keybinding

It caused problems in terminals.
Merge branch 'master' of github.com:bbatsov/prelude
Cask files are Emacs Lisp files
Remove obsolete dep to git-commit-mode
Code style
Remove obsolete markdown module
Extract Helm support into a separate module
[Fix #399] Extract key-chord into a separate module
Fix a reference to nrepl.el