Added `$XDG_CONFIG_HOME/zsh/completions` to fpath for zsh to source
completions from. Any stow modules creating scripts and functions which
should be auto-completable can add their own completion scripts to this
directory for zsh to automatically pick them up.
Add zsh-users/zsh-completions plugin to provide completions for a wide
array of applications (e.g. glances, nvm).
The only file left in $HOME is .zshenv, which sets up zsh to source everything from XDG_CONFIG_HOME/zsh.
Shell files are split into sh and zsh directories, for global assignments (which should be posix compliant, work on any posix shell) like environemnt variables, xdg vars, and global aliases. zsh contains zsh specific customization (prompt customization, plugin loading, zsh completions).
Zsh initialization will pull from sh directory first, loading the respective mirror to its startup file (`.zprofile` loads `sh/profile` and `profile.d/*`, `.zshenv` loads `sh/env` and `sh/env.d/*` and `zsh/env.d/*`, `.zshrc` loads `sh/alias`, `sh/alias.d/*` and `zsh/alias.d/*`)
Once all is done, it will have loaded both global variables, aliases and settings, and zsh-only specifications. Other stow modules, if they want to add shell functionality, can include their aliases and functions in one of the above directories to automatically be picked up by zsh.
