to_snake_case on multiple word keys

[jeremyjh]

I'm pretty sure no one expects underscores to be inserted in separate words. I actually think to_snake_case should only update keys that are in camelCase or PascalCase. Separate words are more likely to be a title, and should not be modified at all.

ProperCase.to_snake_case(%{"Multi Word Keys" => "some value"})
%{"multi _word _keys" => "some value"}