Units: Added Billion Cubic Meters:  BCM, BCM/day, BCM/month, BCM/year
Bug Number: n/a
Release notes (y/n): Yes
For Release Nums: 7.1

Similar to TCM (thousand cubic meters) and MCM (million cubic meters), the 
following entries have been added to the RiverWare "units" text file.  This 
file is deployed within the same directory as the RiverWare executable (or, 
for development, in the directory referred to in the RIVERWARE_HOME_XXX 
environment variable), and is read into the RiverWare program at run time.

  BCM -- Billion Cubic Meters
  BCM/day -- Billion Cubic Meters per Day
  BCM/month -- Billion Cubic Meters per Month
  BCM/year -- Billion Cubic Meters per Year

Here are a couple test screenshots with Series Slots having m3 and m3/day 
units, and exact duplicates of those slots having BCM and BCM/day units.

  http://cadswes2.colorado.edu/~philw/2017/Units/TestPlot-InBCM.png
  http://cadswes2.colorado.edu/~philw/2017/Units/TestPlot-InMCM.png

Excerpt of the units file. (Only the "BCM" units are new):

BCM       Volume   0.000000001
MCM       Volume   0.000001
TCM       Volume   0.001

BCM/day     Flow    0.0000864      perDay    BCM
BCM/month   Flow    0.002678400    perMonth  BCM
BCM/year    Flow    0.031536000    perYear   BCM

MCM/day     Flow    0.0864         perDay    MCM
MCM/month   Flow    2.678400       perMonth  MCM
MCM/year    Flow    31.536000      perYear   MCM

TCM/day     Flow    86.400         perDay    TCM
TCM/month   Flow    2678.400       perMonth  TCM
TCM/year    Flow    31536.0        perYear   TCM

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