Add cubic volumes and oil barrels

Added cubic metres, cubic feet, cubic inches and oil barrels

v0.1.2-alpha

Added millisecond, nanoseconds, microseconds to README.md

Added Force measurements

v0.1.1-alpha

Merge branch 'main' of https://github.com/putridparrot/SwiftUnits int…

An initial release

v0.1.0-alpha

Changed WiP notice