Unified BH_PREEXEC to be called from bash and zsh

- redirection to log happens in lib-bashhub.sh
First shot at writing bashhub update
Edited install script to try to copy old config.
Added contains_element to check if an element is already present in an array.
Use check if already present to evaluate if we should include some scripts.
Backup our user credentials if you're updating we'll just restore them.
After update remove update-bashhub.sh
Prepare for release 0.0.5