- the documentation of .STEX is very rudimentary, it is based on comments in sirstex.F(STXINP).
- changed "*STEX  " to "*STEX I" (for STEX INPUT), in analgy with the other input sections.
- added notes about .VIRTRUNC and .STEX to CHANGELOG (and merged the Dalton 2016.3 section into the
  new developments, we will never release a Dalton 2016.3).