JSX +- toggles like LiveScript object literals

[edemaine]

Inspired by facebook/jsx#134 but with both a true and false version matching LiveScript

[STRd6]

We might want to add ! as a synonym for - in both JSX and object literal contexts.

[edemaine]

I did notice an issue with + and -: because - is a valid part of an identifier, you can't write +foo-bar (it's treated as a single +). Still, I like the symmetry of + and -... Should we leave the possibility of ! for a future PR?

[STRd6]

I think it is correct that +foo-bar is a single attribute. The correct way for someone to work around it would be to add a space. We already have several other places where whitespace around operators is significant.