#1314 – Improve regex filter docstring and avoid compiling compiled regex – python-telegram-bot

This PR improves the docstring of Filters.regex. Changed format to comply with the rest of the file, and specify that pattern can be either a string or a pattern object. Also avoids recompiling regex on regex instantiation.
Add test case and define Filter attribute so sphinx can show the proper message instead of the placeholder text

This PR improves the docstring of Filters.regex. Changed format to comply with the rest of the file, and specify that pattern can be either a string or a pattern object. Also avoids recompiling regex on regex instantiation.
Add test case and define `Filter` attribute so sphinx can show the proper message instead of the placeholder text