GitLab

- Cleans out aliases.zsh.
- Removes unneeded cd function.

Those aliases should be in user's .zshrc file, instead of being default.

Modify directory listing aliases to make more sense. Remove conflicting helper
function (mcd conflicts with mtools).

Also an alias for the function.

The ll alias is a very common default for bash in Linux distributions, so use
that definition.

Initial implementation of a new plugin system, so that people can managed which aliases/functions they want.

Moving all zsh config options into a lib/ subdirectory to make way for some upcoming changes to directory structure and configuration options