Python: Add support for attributes in hooks

Would like feedback/testing on the changes. 

I couldn't find an easy way to add attributes to the callbacks like was possible with javascript so it adds the *_attrs* version of the hook functions just like the C api and ~~it just adds *emit_print_at* to include the time instead of forcing them to create an attributes object each time~~ emit_print() takes optional keywords for attributes.

Here is a script I wrote using this - https://github.com/TingPing/plugins/blob/master/HexChat/mymsg.py