v2.0.0

Lots of breaking changes in every geometry, only the major ones listed here:

• tran2 is replaced by plane2 and helm2 to separate passive and active transformations.
• proj2 is replaced by transitFrom, transitTo, and projectTo functions for each geometry.
• vector2 is renamed to vec2

New geometries:

• plane2, plane3
• helm2, helm3
• line2, line3
• point3, vec3

New features:

• perspective projections for multiple geometries. See projectTo functions for details.

Other changes:

• improved documentation, lots of fixes
• improved introduction with illustrations
• comprehensive test suite