Added support for upper case values parse

[viniciusls]

Hey,

It'd be cool if your lib parse the string value to lower case during the comparison because people can send TRUE or FALSE values or even True or False. I thought about saving the .toLowerCase() value in another variable to reuse but I guess it wouldn't be worth creating another var just to reuse in two lines. I also thought about converting 0 and 1 (both string and number) to bool, but I understand that the package will not have control on where it should parse it or not (the user may actually need it as a numeric value instead of bool), so I leave it untouched.

Thanks!