Support common ways to config babel

[chinesedfan]

As suggested in #228, hope this processor read babel configurations from .babelrc or package.json.

Something needs to be confirmed:

• are there other config ways should be considered? Like unnormal path of .babelrc.
• should deprecate options.parserPlugins in future?
• how to keep the current feature that .ts files will use typescript and others will use flow?