Use full digest length instead of just one byte.

When our universal hash function fell back to MD5 for inputs larger than
supported by H3, the computation only returned the first byte of the MD5 result
instead of as many bytes as needed to cover sizeof(Hasher::digest).
Switch to double hashing.

For large k, standard hashing imposes an unnecessary overhead. By switchting to
double hashing, we invoke the hash function code at most two times.
add new TLS extension type numbers from IANA
Merge remote-tracking branch 'origin/topic/matthias/bloomfilter-fix'

* origin/topic/matthias/bloomfilter-fix:
  Switch to double hashing.
  Use full digest length instead of just one byte.

BIT-1140 #merged
Merge remote-tracking branch 'origin/fastpath'

* origin/fastpath:
  add new TLS extension type numbers from IANA