Add '--pattern' parameter to specify a regex trigger

[nicobo]

Currently there are :

a. commands to explicitly translate a text
b. keywords to implicitly translate the whole message containing them

Keywords are simple words that are :

1. translated into any known language
2. transformed into a regex

Allow specifying directly the regex that will trigger an implicit translation, rather than a indirect list of keywords.
Keywords should then just be a input to generate a list of such patterns.