Version 3.0.0-beta.1

General

• Move core code out of the index file and into its own file. This is so
  that the index file can be used strictly for exporting
• Add exports for all measures from the index file in definitions
• Remove unit property from Anchor
• Update measure structure and Convert class to support any system name
• Update measure structure and Convert class to support any number of systems
• Update Convert class to support generics types for Measure names,
  System names, and Unit names. This provides TS with enough information
  to warm users if they are trying to use a unit that doesn't exist (for
  example)
• Update Convert class to throw an error if system anchors are missing

Measures

• Fix descriptions for cm2 area unit