Support custom babel configuration

[schibrikov]

A lot of people are using various proposal plugins for babel. react-gettext-parser is unable to parse files using some additional syntax.
We need to just add more plugins to .babelrc to support common cases or, more preferably add support for custom configuration.

[alexanderwallin]

Yes, this would make perfect sense. Ideally, react-gettext-parser would just pick up whatever Babel configuration is available.

[schibrikov]

@alexanderwallin can we just add some proposal plugins for now, so I can start using this tool, and then start working on auto picking up project's .babelrc?
It fails on parsing "export default from" and maybe "export * from" for now.

[alexanderwallin]

If that's easy to setup, then sure. Would you be able to submit a PR?

[schibrikov]

Yes, of course. I'll try when I get some time.

[schibrikov]

Finally I found some time to make a PR. Now it is possible to parse my entire project.

I made a quick research about picking up external babelrc:
The thing is .babelrc and this plugins list are 2 different kind of things. Here we specify plugins used for parsing (for understand syntax), but in .babelrc files we see a list of transformations that will be applied, not a list of used syntactic constructions.

For example those users who support only latest browsers (chrome canary) can leave this list empty at all. And if we'll make a list of plugins according to .babelrc, out parser will not be able to parse code at all.

The same issue exists in babel-eslint project (babel/babel-eslint#573).
Seems like it is not being solved for almost a year. But looks like they have added an option to specify extra plugins used alongside with predefined.

[alexanderwallin]

Thanks for the PR and clarification! Let's just keep it static for now, then. If things break, people can report it and we'll have another look.