Add operators to perform calculations using the math/hobby module.
Allow names to begin like existing non-splitting tokens.

e.g: `Skew` is an operator and `SkewTransform` is an allowed name.
Parse 'Infinity' as a number
Allow negative indexes in :i pseudo class selector.
Merge pull request #247 from graphicore/improvements-for-formulae-language-and-selectors

Improvements to formulae language and selectors
Fix rembering of 'lastVector' in MOMPointPen
fix reading of skeleton on-curve point, formatting
fix: make jshint pass
remove outdated detail
better structured skeleton drawing code
Use Vector instead of Complex

Complex should be treated as an impplementation detail, it has no
semantic quality in here.