RuleSet::addRule() insert position support.

[IceReaper]

I'm currently using this lib to auto-prefix css rules for a wider browser support without the need to manually add all those rules. This requires me to add the new prefixed rules before the unprefixed one. I Made some additions to allow you to specify the exact location where the final Rule should be:

[sabberworm]

Cool, thanks.

Could you add a few unit tests for this feature?

Also, I think the API could be simpler: append the rule to the existing rules if $oSibling is null, prepend before $oSibling othewise. This way, any position can be adressed and we don’t need $bPrepend at all.

[FMCorz]

@IceReaper Do you have that library to auto-prefix CSS lying around? I'd be interested in it.

[IceReaper]

@FMCorz Sorry, left all the sources with my old employer, got a new job and have no longer access to them. Sorry :(