Add CRAM 3.1 (PR #433)

- Added CRAM_codecs document to describe the proposed CRAM3.1 codecs.

  This also has the CRAM3.0 rANS codec in it which has been removed from
  CRAMv3.tex.

- Update CRAMv3.tex to include both CRAM 3.0 and 3.1.  The differences
  are so minor it's essentiall just expanding the list of legal values
  in Block compression methods and updating a few 3.0s to be more general.

The new EXTERNAL compression codecs added for CRAM 3.1 are:

- rANSNx16.  16-bit renormalisation instead of the old 8-bit
  renormalisation, for extra speed.  This now permits either 4-way of
  32-way unrolling, with the latter being a good target for SIMD
  optimisations.

  The newer rANS also includes PACK, RLE and STRIPE (interleaving)
  transformations to be applied prior to entropy encoding.

- Adaptive arithmetic coder.  This has all the same transformations of
  rANSNx16, but with slightly better ratio and better performing on
  data sets with non-stationary probabilities.  It's slower however.

- FQZComp quality codec.  A generalised version of the old fqzcomp-4.6
  tool.

- Name tokeniser.  A compression tool for any data series that has
  repeated structured text elements.  It breaks the line down into a
  series of tokens and optionally deltas each against a previous
  line.  Each token them forms a new series of compression streams,
  which are in turn compressed and serialised into a single block.

With thanks to Michael Macias and Yash Puligundla for review and
corrections.

Author: jkbonfield