[twitter] follow timelines while hastags querying
[twitter] improve tests
browser2: More specialized exceptions

and extend common exceptions
browser2: Add RawText filter

Allows getting .text of elements without any alteration.
This is useful for at least textarea and pre tags.

Maybe the .join character should be configurable.
pastealacon: Fully use Browser2 filters

This also transforms the fill_ function into both a filling and a getting
function. Magic!
browser2 filters: Force unicode, little style fixes

lxml for Python2 has the tendency to return str instead of
unicode when the contents are pure ASCII.
Try to fix the nonsense.