Clamp hashable dep below 1.2 (it's still broken), fix the benchmark, bump version.
Ignore TAGS and generated csv files.
Use smaller hash codes to go faster and save space.

Before, in the basic and cuckoo hash tables, we were storing full
machine-word-sized hash codes in the table so that we could quickly search a
whole cache line for a key (or a combination of keys) without branching.

It turns out that a full machine word is not really necessary for this
application; switching to a 16-bit key will very slightly increase the number
of hash collisions within buckets (meaning that we'll compare more keys), but
will pay big dividends in terms of:

  * reduced wastage of RAM

  * searching more keys at once, allowing buckets to grow bigger

  * more cache hits on the hash codes array.

Preliminary results suggest a reduction in table overhead of about four bytes
per key-value pair (on 64-bit) and speed increases around the 15% range,
although I need to re-run these results and probably do some tuning afterwards.
Adjust to work with GHC HEAD
Add benchamrking results