Allow pars escaped surrogate pairs

[fiserro]

Surrogate pairs are parsed as two 16bit chars instead of one 32bit char.
For example this Json contains two 32bit emojis:
[ { "id" : "1", "message" : "\uD83D\uDE0B\uD83C\uDF70" } ]

We'r using java faster xml lib on one side FasterXML/jackson-core#223 and nodejs jsonparse on the other side.

There is a diff with fix:
diff.txt

[fiserro]

I can make a clean pull request. The diff is just for inspiration how to solve it.
@creationix

[creationix]

Could you please make a pull request? Thanks.

[fiserro]

#33 @creationix

[fiserro]

@creationix Thanks for merge #33. When we can expect the new version?

[creationix]

It's live! Published to github and npm