7.1: Dec 3, 2018

• Import definitions.unit 2.44 from units 2.18 with 36 new units.
  When upgrading from a previous install, use SELECT unit_load(); to import.
• Adjust powers.h to round "1" down by one ULP.

6.0: Mar 7, 2018

• Add @@ operator: similar to @, but returns the value of the resulting unit
  as double precision number.
• Fix parsing of addition/subtraction in unit values.
• Grant SELECT on unit prefixes and units table to public.
• Add unit_load() function to load/update the data tables.

• Add rounding function.
• Import definitions.units from GNU units 2.16 with 70 new units.