Fix header sizes

Outgoing SYN_STREAM and HEADERS frames got
incorrect sizes.
on_stream_close when receiving FIN data frame

When receiving a data frame with FLAG_FIN, and
we already have closed the stream in our end,
call the on_stream_close callback.
Merge pull request #4 from krestenkrab/700b06d329a40ba38a491166793fb7af69f5236b

Two more fixes