Merge branch 'next'

* next:
  test, provide regression for empty ute files, impl'd via empty uta mux
  hygiene, rely on stat object once only
  fix, make sure sluts start behind the header, truncate the file if necessary
  minor, support reading vol-candles
  minor, redef vol candles as V+VWAP+TWAP
  minor, support printing vol-candles
  minor, support each and every tick type in uta printer
  test, adapt to recent major changes
  major, swap g32 and bidask, so that the generic ticks have lower 3 bits set
  major, redefine tick types 11 to 15.  11 being OI, 12 g32, and 16 g64
  minor, formally define vol candles