Add hook before/after twgit command to execute shell script

[chemidy]

We need the possibility to execute shell script before/after twgit command.

• Example with : twgit release finish

We need to launch a shell script to tag the version on a file, and launch composer update, commit additional data, ...

• Another Example with twgit feature start 1234

We need to launch composer update each time we switch on a feature.

So, i will add the possibility to launch script files for each command before/after twgit command.

To use this hook, we just have to create a .twgit directory on our project, and add new shell scripts with the right name.

twgit_hook_release_after.sh twgit_hook_release_before.sh twgit_hook_feature_before.sh twgithook....