beginnings of bulk support

Start supporting bulk requests (insert and delete).
The format is newline separate operation/data entries for inserts and newline separated operations for deletes (see http://www.elasticsearch.org/guide/reference/api/bulk.html). I've exposed a post-string method in rest to allow this as I can't see a way to force newlines from a single call to json/encode.
Currently document/bulk doesn't take an index/type and these have to be specified in each operation. The ES docs suggest that if they're specified in the bulk url then they should be used when they're not present on the individual operations, but this doesn't seem to work for me. I'll add some more specific tests to see where the problem is, but until then it's fine just to pass index/type in the operations.