Implement header (and footer) support

[doowb]

This PR implements emitting a header and footer event with data that comes before and after the specified path. This is implemented in a way that when the specified path is first found, if the header object has been populated, it's emitted immediately so the entire document doesn't need to be read in.

The footer contains the remaining properties (if any) after the values in the specified path have been exhausted. I believe my logic is correct since the current tests are still passing.

I think this address #99 and #93.

I tried to keep with the current coding style, so please let me know if there is something that I need to change.

Thanks!

[dominictarr]

thanks this looks like a great pull request, will merge. do you mind if I also add you as a collaborator?

[doowb]

do you mind if I also add you as a collaborator?

I don't mind, that'd be great. I'm happy to help out where I can.

[dominictarr]

awesome, you are now also a collaborator and npm owner,
merged into 1.2.1

[jcready]

Can someone explain how we can use these new header/footer events to take JSON data like in #93 and pipe it to a write stream such that I can modify each object in the records array but also include the rest of the top-level properties in the final output piped to the write stream?