Implement HTTP/2 Draft 13; HPACK Draft 08.

Closes #945 

Notably increases setting id from 8 to 16 byte, drops spurious frame types, accepts unknown frames, simplifies padding.

Tested on twitter

```bash
$ okcurl/target/okcurl-2.0.0-SNAPSHOT-jar-with-dependencies.jar --frames -X HEAD https://twitter.com
>> CONNECTION 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a
>> 0x00000000     6 SETTINGS      
>> 0x00000000     4 WINDOW_UPDATE 
>> 0x00000003    60 HEADERS       END_STREAM|END_HEADERS
<< 0x00000000     0 SETTINGS      ACK
<< 0x00000000     6 SETTINGS      
>> 0x00000000     0 SETTINGS      ACK
<< 0x00000003   675 HEADERS       END_STREAM|END_HEADERS
>> 0x00000000     8 GOAWAY
```
Ah, cool.