Babel 6 compatibility

[megheaiulian]

There is backward-incompatible change from Babel 5.x to 6 as stage option is replaced with presets.

[gpbl]

Yes, the source code is not yet using Babel 6. I wonder is this a problem?

[gpbl]

I'm trying to upgrade to babel 6 in #99. @megheaiulian care to explain your experience? Because I also have some problems :)

[megheaiulian]

@gpbl
It seems that if you just setup a correct .babelrc the code is already compatible with Babel 6.
I see you get a lot of errors in your pull request. Try maybe to use only babel-preset-stage-0 ?

[gpbl]

I have no idea. It seems everything is right there.