[BUGFIX] Always use strict comparisons

* use the "strict" parameter for in_array
* use ===/!== instead of ==/!=
* make sure that parseNth always returns an array of integers
* fix an incorrectly placed parenthesis in getCssSelectorPrecedence

Closes #109
Merge pull request #125 from jjriv/bugfix/strict-comparisons

[BUGFIX] Always use strict comparisons