Before I switched to Fresh, I assembled my dotfiles with my own script
that ensured this was set, but it is no longer set. I don't need the
dot files directory to be customisable, so I'll just hard-code the path
Changes:
* Reduce duplication across Bash and Zsh
* Increase code sharing between the two
* Automatically load shell files in 'lib' directories
* Zsh `precmd` emulation in Bash
* Move shared prompt (not compatible with Bash) to be Zsh only
* `rbenv` loading for each shell
* etc...
Still to do:
* Bash prompt
* Cross-shell terminal color abstraction