Alias, variable and function allowed characters unification

Aliases, variables and functions consist of [a-zA-Z_][a-zA-Z0-9_-!]*

Also, if you define an alias you can now show its definition like this:

> alias gc!="git commit --amend"
> alias gc!
alias gc!='git commit --amend'
> alias noalias
ion: alias 'noalias' not found