Update hook documentation

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Drop unnecessary code

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Constify and staticify methods

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Use working tree root as CWD for hooks

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Initialize out params of hook methods the same way everywhere

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fix broken build

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>