json5 support: ObjectExpression and Property nodes

Hi there,

I needed to be able to use jsons in the middle of the evaluated expressions.
I added support for esprima's ObjectExpression and Property nodes; 
json, json5 property names and values can be expressions are correctly parsed.
For example: `{ ("foo"+1): DATE(3), "oh": { nested: [ 1, 2+3, 3 ] } }` will generate properly.

Thanks for a very nice and small parser!