Add parseSource method

[Radiergummi]

This PR adds support for parsing source strings instead of file paths. Therefore, it exports two methods: parseFile and parseSource. It would be easy to keep the parse method in main.js as an alias to parseFile to preserve compatibility.
This feature is quite helpful for documentation generators that process files in separate modules at an earlier stage.

Note: Please ignore the README changes, they are specific to my fork.

[rafaesc]

Hi @Radiergummi, thanks for PR,

I would like to know why you want parseSource, I think that isn't necessary because parsing extract the source.

Regards

[Radiergummi]

Hi @rafaesc, I am working on a documentation framework called Phoenix that splits reading, parsing and writing in separate steps, basically. I know this might sound like a pretty special use case, but considering the change is around 20 lines of code on your side and is not a breaking one, I think it wouldn't hurt to add a little flexibility.
I'd be happy to write the tests for this too.

[rafaesc]

Hi @Radiergummi,

Nice work, ok, I will update this repository for fix an issue and the same time I publish your changes.

Regards,

[Radiergummi]

Alright, that's perfect, thank you so much! I'll credit you in the Readme once the VueComponentParser is ready 😊