Fix wrong LS_COLORS syntax

Also add 3gp that disappeared in later commit.
Add git repository information in PROMPT

Inspired from git-prompt plugin of oh-my-zsh, here:
https://github.com/robbyrussell/oh-my-zsh/tree/master/plugins/git-prompt
Do not print history command number
Simplify using chpwd(), precmd() and preexec()

Instead of an array to be evalued by zsh and call functions.