Added CurrencyFormatter with unit test
Removed undeeded code comments
Added basic PercentageFormatter with unit test
Changed Decimal and Percentage formatters so they now allow you to specify a thousand separator as a fourth argument to format()
Added percentage formatter to Formattr so it can be called using formatPercentage(). Also added a static method to access Formattr::decimal()
Added static method to access Formattr::number() with associated unit test
Added a helper functions file so static methods can be called even more easily + unit test for decimal() global function in the helpers.php