Add an option to skip camel casing keys

[adamgruber]

The default behavior of this plugin is to camelCase variable keys during the transform.

$my-variable-name: 10px //=> myVariableName: '10px'

This may be undesirable for some so an option to skip this part of the transform would be a good idea.

[adamgruber]

v0.2.0 introduces options support including a camelCase option. Setting this to false will skip the camel case transformation.

[Coord]

It looks like this option is not working with nested objects.

[adamgruber]

@Coord Mind opening a separate issue with some more details and code to reproduce?