modularized nth-checks, moved all dom functions to DomUtils
avoid early returns, always return bools + simplifications

most notably: getSiblings now always returns an array
moved parsing of nth-checks to its own function
moved attribute selectors to lib/attributes.js
moved pseudo-selectors, general rules & the sort function to their own files

also changed some names
[attributes] only call hasAttrib when actually needed

improves usage of inline caches
[nth-check] renamed `baseFuncs` to `BaseFuncs`
[index] added a parseConditional function, fixed comment
[general] moved requires to where they are needed
[index] renamed `parse` to `compile` and `CSSwhat` to `parse`
[index] be smarter when combining functions