Implemented value array prefixing (mutation)

[rtsao]

Fixes https://github.com/rofrischmann/inline-style-prefix-all/issues/13
Implemented with forEach and mutation #14 (same thing but with map/reduce)

In theory, this should perform better, though it's actually slightly more lines than #14

[robinweser]

Awesome thank you! Would love if you could remove the semicolons to keep it consistent. Also you might add some line comments to describe some steps, but I guess it is nothing which one would not understand while reading.

I will merge this after semicolons are removed :P

[rtsao]

Oops! Totally forgot about your style ;)

[rtsao]

Gentle bump :)