CRAM specification

My first draft of TeXifying the CRAM specification is now in place.

It went suprisingly well after exporting Google Docs -> .docx -> RTF (in word) -> rtf2latex2e -n -> sed script hackery -> manual tidying up. :)

Could Vadim, and maybe myself, be added to the primary samtools/hts-specs commit permissions as Vadim is the primary maintainer of the specification document. Thanks.