correct definition of dram, per CEG-308566, and add definitions

While the fluid dram specification is ok, the plain dram is:
* an avoirdupois unit of mass (and so should not be based on fluid ounces) [1] [2]
All references to the use of dram as a fluid measure call it a 'fluid dram' (and make it 1/8 fluid ounces).  

This changes the definition was changed and moves the result into the mass section.

[1] National Institute of Standards and Technology (October 2011). Butcher, Tina; Cook, Steve; Crown, Linda et al. eds. "Appendix C – General Tables of Units of Measurement", page C-6
[2] WIkipedia entry https://en.wikipedia.org/wiki/Dram_(unit)