Don't inline "non-selectors" from "non-used" files

[theKashey]

Right now used-styles inlines everything it can't "match" - font declarations and animations. However - it might do it only for the limited set of files, which might be known from the "bunder integration" for example

It's already partially supported via filter filters in different APIs, and should be just better documented and tested

• shares the implementation with https://github.com/theKashey/used-styles/issues/14