Remove all usages of contrib.
fixed bug in unary - operation
added deg units
create colors with 3 integers
better unit tests
Better data structures, and splitted in two ns.
added value operations
utility functions to create values. Fixes...
no prop call needed in rules and mixins
no vectors on prop
introduced Color type and helper to create it
added multiple value props, and length symbol helpers
mixins with nil elements supported
added mixin function to group rules and props