2.2.0 AST cloning, improve partial merge and bug fixes

• Implement AST cloning by adding clone() function and clone option for compress() function (#296)
• Fix parse and translate attribute selector with flags but with no operator (i.e. [attrName i])
• Don't merge rules with flagged attribute selectors with others (#291)
• Take in account functions when merge TRBL-properties (#297, thanks to @ArturAralin)
• Improve partial merge (#304)
• Tweak scanner, reduce code deoptimizations and other small improvements