The options were never really used and do not seem especially useful;
initialization with a seed file still works.
This also fixes a bug with the initialization of the siphash key.
This commit mostly changes the hash function that is used for Internal
hashing of data < 36 bytes from H3 to Siphash. This change is motivated
by the fact that it turns out that H3 apparently does not deliver a very
good source of data uniqueness; running HLL with H3 as a hashing
function results in quite poor results (up to of 75% off in my tests).
In difference, running HLL with Siphash (or HMAC-MD5) changes this
factor to ~2%.
This also fixes a long-standing bug in Hash.h which truncated our hash
values to 32 bit on most machines.
Furthermore, it once again fixes a problem with the Rank function in
HLL.
