Replace pythonz with pyenv

Depending on Python to manage Python is silly.
Add utility aliases for Cygwin

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Remove duplicate alias definitions
Simplify a conditional
Do not define $GEM_HOME

Defining it breaks gems for all users who neither use RVM nor rbenv,
but have a different default Ruby version nonetheless.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Use correct option for pacman search aliases
Stop module loading when external code fails to source
Comment an unnecessary style
Add `custom` folder plus scripts and aliases.
Activate custom scripts and customise `.zshrc`
Add `prompt_jakob_setup` file and activate prompt.
Customise `zshenv`.
Customise `zpreztorc`.
Update external modules
Update alias definitions.