rbenv: speed up initialization
dotfiles: aren't checked out as ~ anymore
zsh: use Terminal.app's default for backspace
alias: no longer using twitter CLI
zsh: fewer PATH customizations

* ./bin - boxen does this for us
* $HOME/bin - don't use ~/bin anymore
* /usr/local/bin - /etc/paths does this for us & boxen has homebrew in /opt/boxen/…
zsh: ~/src shortcuts
clang: downgrade 'unused-command-line-arg…' to a warning