Combine all quantity modules into one huge Quantity module?

[ianmackenzie]

Pros

• Only one module to import
• Less risk of module naming collisions
• Unified namespace for operators: Quantity.sin instead of Angle.sin
• More understandable naming for pixel-related functions: Quantity.pixels, Quantity.inPixels instead of Pixels.pixels, Pixels.inPixels

Cons

• Breaking change
• Huge module documentation page to try to browse through
• Could basically be accomplished by module aliasing instead (with a few function renames to avoid conflicts)
• Doesn't play quite as nicely with defining custom units/quantity types (would have to 'merge' those with the main Quantity module, which can be confusing)

Required changes

• Rename Mass.pounds/Mass.inPounds to poundsMass/inPoundsMass to not conflict with Force.pounds/Force.inPounds
• When Add minutes/seconds support to Angle #21 is implemented, use arcminutes/arcseconds instead of minutes/seconds

Since Temperature would still be a separate module, could have both Temperature.degreesCelsius (temperature) and Quantity.degreesCelsius (temperature delta).