[TASK] Add a comment about a protected method

addStyleElementToDocument is protected instead of private on purpose
in order to allow overrinding in subclasses.

This change adds a comment to provide this information so that it will
stay protected even during code clean-ups.

Closes #122
[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
[CLEANUP] Use "int" and "bool" in PHPDoc

"int" and "bool" instead of "integer" and "boolean" are the more common
form and also the default in PhpStorm.

Closes #126
[TASK] Cast to int instead of using intval

An (int) cast provides better performance than an intval() call.

Closes #128
Merge pull request #124 from jjriv/cleanup/protected

[TASK] Add a comment about a protected method
Merge pull request #125 from jjriv/bugfix/strict-comparisons

[BUGFIX] Always use strict comparisons
Merge pull request #127 from jjriv/cleanup/short-types

[CLEANUP] Use "int" and "bool" in PHPDoc
Merge pull request #129 from jjriv/cleanup/intval

[TASK] Cast to int instead of using intval
[TASK] Switch the coding style to PSR-2

Also update PHP_CodeSniffer to 2.0 as this version provides the
corresponding standard.

Closes #102