Fix the alert command

Closes #23
Fix the GitHub regex
Add priority support
Remove trailing whitespace
Add default responses to the repo handler
[repo listener] Avoid useless repo when 404
Remove unnecessary line
Fix photo handling for Twitter
Do not load all plugins by default

This way the user can cherry pick only the modules he wants.

Run make bootstrap to activate only the required core modules.
Print full stack traces on errors
Add full-bootstrap to add all listeners & plugins
Fix the unstandard ln arg in the Makefile
Update README.md
Add reverseau listener