Added tag to snapshot, generate XML

XML description of registers and snapshots is written on build.
Update filename of generated system info.
Bitsnap block - bitfield for extra value.
Missed a munge-block in the init of bus_expand.
Latest QDR CT added to CASPER Reorder library.
Merge branch 'master' of github.com:ska-sa/mlib_devel
feedback_osc optimise

Reference tables combined into single lookup table to reduce BRAM use with
large numbers of reference values.
commit 7765ddf redo

recursive merge with 7765ddf left working .mdl but block may have been compromised.
Copied block in.
commit 86399b6 redo

recursive merge worked but blocks potentially compromised.
Copied bitsnap and bitreg in manually.
commit 727e0b9 redo

qdr_ct readded manually as recursive merge may have damaged it.
commit 86399b6 redo

snapshot block readded manually to ensure no damage from recursive merge.