rename CommandHandler._dispatch to CommandHandler._dispatch_trigger
handlers 'commands' attribute is now a class attribute + add_handler now takes a class and not an instance
use EVT_* variables to define events + do triggers validation in __init__
minor changes
modify handlers docstrings according to latest changes
store log and date format in globals (reusability)
PEP8
fix misplaced modification + pass command args as string
reflect recent changes on sample bot
no longer strip trigger from messages args - fixes #4
define a URL global variable containing link to the github page
reflect latest changes in documentation