Add internal cmtk.version function
Fix: xformpoints + some compound CMTK registrations

* there is a bug in versions of CMTK<3.2.2 for streamxform-based
  transformation of some compound registrations. See:
  https://github.com/jefferis/cmtk/commit/209168d892d8980e47
  for details.
add tests for cmtk.version()
document and export cmtk.version
also document nat.cmtk.version option
CHECK: partial arg match fix
Bump version to 1.5.9