Fixes #356 - leaving out IE7 *+html hack if ie7 compatibility mode.

* Also removes *+html hack from multi-selectors.
Fixes #359 - handling escaped double backslash.
Fixes #354 - !important overriding in shorthands.

Follow up to #346 for overriding important property by another important one in shorthand declarations.
Fixes #358 - property merging in compatibility mode.

* More understandable properties can't be merged into less understandable shorthands.
* E.g: div{background:linear-gradient(...) #000;background-color:red;}
Version 2.2.16.