This change adds onChunkCallback to the request. If defined it will be
called repeatedly with the incoming data. This allows to process data on
the go or write it to disk instead of accumulating the data in memory.
* introduce send fragment
* can pass a fin frame
* can send messages which are a perfect multiple of the chunk size
* set fin only for last fragment
* cleanup
* last fragment should be of type CONTINUATION
* Add simple send and receive programs
* speedups receiving + better way to wait for thing
* receive speedup by using linked list of chunks instead of large array
* document bug
* use chunks to receive data
* trailing spaces
