remove HTML from readme
use injections in XSemantics
move subtype rules in own new XSemantics system

Also improve default subtype rule by Using EClass.isSuperTypeOf()
add intermediary CommonType XSemantics system
update to xtext 2.6.0 and xsemantics 1.5.0
add class for complex numbers and number helper class
add syntax and typing for complex numbers
mark MatrixTypeUtils as deprecated