shell: Update to latest oh-my-zsh
tmux: Fix vim detection for smart split navigation

It would detect anything with the substring "vim" as a vim window.
tmux: Show guard status in bottom left of tmux status bar
vim: Remove explicit <C-hjkl> keybindings, handled by vim-navigator.
vim: Don't map <C-jk> in NERDTree
vim: Use rbenv's ruby for syntax checking in syntastic.
vim: Use git ls-files to list files for CtrlP inside a repo
ruby: Generate RDoc/RI for installed gems again