Small speed increase - only attempt to compress the CORE block when it
is of sufficient size to make it worth while.


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3680 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
Added support for compressed SAM headers.

This involved removing the various #ifdefs for different types of
padding and instead coding it up with a variable that changes
depending on CRAM v2.1 or v3.0. (Cramtools doesn't allow for a second
padding block in 2.1, although technically it could fit within the
existing spec.)



git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3681 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1
Replaced RANS0 and RANS1 codec identifiers with a single RANS
codec.  Internally we still call them RANS0 and RANS1 methods so it
can auto-tune to order-0 or order-1 in the statistics, but before
writing out we force both to be RANS/RANS0 identifier.

The rANS implementation has therefore added an extra byte (order) to
the data stream.  I also tweaked the efficiency of decoding a bit more
so it's now faster.


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3682 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1