Refactor units

[jesper-friis]

Refactor and update the unit modules to the following structure:

• Modules for categorising units:

  • sidimensionalunits: A module with classes categorising units according to their SI physical dimensions.

• Modules with SI units:

  • siunits: The 7 base units and 22 derived units as well as the metric prefixes specified in the SI system.
  • prefixedsiunits: SI units made of a metric prefix and a SI base, derived or accepted unit. Examples: km, mg...
  • coherentsiunits: Coherent SI-units. Products of integer powers of the base and derived SI units. Examples: A/J, Nm, m³, ...
  • noncoherentsiunits: Non-coherent SI-units whos numerical factor in front of the product of base SI units is NOT equal to one. This include all SI-units not included in the modules above. Examples: g, mg/s...

• Modules with non-SI units:

  • siacceptedunits: The 15 non-SI units that are accepted for use with SI.
  • siacceptedderivedunits: Non-SI units that consists an optional metric prefix followed by a product of integer powers of the base, derived and accepted SI units. The product must include at least one SI-accepted unit. Examples: km/h, kWh, MeV, etc...
  • specialunits: Non-SI special units. Examples: Day, Week, Bar, Inch, ...
  • otherunits: All other non-SI units that does not belong to any of the modules above.

• Additional modules:

  • unclassifiedunits: Units copied from QUDT that has not yet been classified in one of the above modules.
  • deprecated: Units classes that have been deprecated - typically because of change of IRI.

Make the prefixed unit classes independent of SI to avoid inconsistencies for non-SI units with a metric prefix like kBar.