ENHANCED: Modernised library(shell), so we can use it in unrestricted
SWISH shells for administrative tasks.
ENHANCED: Make statistics/0 use print_message/2 and added statistics/1,
returning a dict carrying the same information and thread_statistics/2.
ENHANCED: threads/0, join_threads/0: use print_message/2.  Output of
threads now includes time and stack usage.
ADDED: statistics/2 keys =epoch= and =process_epoch=
Added thread epoch to info.
Allow thread_statistics/3 and thread_property/2, provided we ask for
the calling thread.
Added epoch to statistics data.  Declared statistics/1 as safe, so we
can use statistics/0,1 in SWISH.
Added \dictitem to manual instrastructure
Updated http, ltx2htm and pldoc
FIXED: sandboxed meta built-ins with non-meta arguments.
Updated pengines.
Updated xpce