Feat: Ignore case

[NickBolles]

I was confused by the lowercase option because I thought it would match something like NODEENV env var to nodeEnv class member. It makes sense now that it's meant for env vars like NODEENV (or some mixture like NodeEnv to map to a class member named nodeenv

Even just an example would be more helpful, but adding another option to normalize the capitalization of both the env var and the class member would be helpful I think. then I can have class members that are in camel case (nodeEnv) and also have mixed case for env vars. Having the exact capitalization is a little tedious.