Fix a bug in Update(Chunk)

If there is not enough bytes in the input to finish the current block, just
consume all the input and stop.
Update comments and fix a typo
Optimize Hash(Input, Key).

Use Update(Chunk) instead of calling repeatedly Update(Byte).
This optimization corrects the negative effect of the
commit 1e8c7e6dab7692e281d73d14067d3f7ad46beb4d on the use case 1.

Time used to process ~440MiB of data with SipHash-2-4
-----------+------------+------------
| Use case | Before (s) | After (s) |
-----------+------------+------------
|    1     |   5.090    |   0.437   |
|    2     |   1.134    |   1.127   |
|    3     |   0.487    |   0.466   |
-------------------------------------

As a reminder, the use case 1 is: hash the whole data in one pass (Block mode).
Update version number.