improve first-of-type, last-of-type, nth-of-type, nth-last-of-type pseudo selectors
tests for *-child selectors with class
add tests for *-child pseudo selectors with classes
fix all *-child pseudo selectors when used with a class and remove need for preprocessing the node tree
Merge pull request #968 from twalpole/of-type

improve *-of-type and *-child pseudo selectors