Make component source string replacements optional

[naturalethic]

As the string replacements were causing invalid source when given a pure component such as

export default function MyComponent() {
  return <div>Hello</div>
}

and turning them off seems to work just fine, provide an option to do so.

[ondrejbartas]

@naturalethic thank you for PR, can you add some comment to Readme pls?

[naturalethic]

Ok I added some info there -- sort of hard to explain though because I don't know why you're doing that mangling in the first place.

[ondrejbartas]

we were doing those replacements because some babel transpile files weren't able to be processed by react-docgen