Add some common modifiers

Their syntax is somewhat ugly, but I just can't figure out how to support informative repr in a better way.
add flags to re modifiers
Fix modifiers' repr format for kwargs
Fix lang_utils' imports
Fix Title/Text modifiers
Rewrite modifiers with fancy decorators
Add introduction docstring
Add possibility to pass compiled regexp to modifiers
Add common modifiers' docstrings
Merge pull request #4 from hatbot-team/modifiers

Add some common modifiers