adblock: make keywords part of the rule itself
adblock: refactor AddRule into AddRule and addHide
adblock: add explanations to mergeOnSelector and mergeOnDomain

The reason for mergeOnSelector, and the order in which mergeOnSelector
and mergeOnDomain may be called is important but not instantly obvious.
Document it.
adblock: in mergeOnDomain, use struct instead of string concat for key
em: rewrite line parser

The old parser was overly complex and had several hard to diagnose bugs.
For example, it did not the argument count correctly and it didn't strip
quotation marks correctly in all cases.
add uzbl instance to event

Provide uzbl.Uzbl, which is a wrapper around event_manager.Event,
additionally carrying the uzbl instance for which the event occured. On
the long run, this will allow plugins to handle multiple instances at
once, which is especially important for the adblocker.
enforce vanity import path