Added support for generating logarithmic units

- "Logarithmic" and "LogarithmicScalingFactor" are used in the json file to indicate the unit is logarithmic.
- Added a separate PowerShell script to generate the logarithmic arithmetic operator source code.
Added support for generating arithmetic operator unit tests for logarithmic units
Tweaks to logarithm PowerShell scripts

- Added documentation to logarithmic source code generator functions.
- Tweaked various comments and names.
- Inverted logic when checking if a unit is logarithmic so it's easier to read/understand.
Removed auto-generation of logarithmic addition and subtraction unit tests

- The previous calculation is incorrect in certain situations. There's no way to define the expected value without re-implementing the addition/subtraction algorithm.
- Developers are now responsible for creating custom logarithmic addition and subtraction unit tests.
Merge pull request #45 from bretthysuik/feature/logarithmic-units

Feature: Added support for generating logarithmic units