core: refactoring PVector protocol & splitting out PNormalize, PMagnitude, PDistance & PReflect, adding extrude-shell to PExtrudeable, adding subheadings for protocol impls
core: refactoring PVector protocol & splitting out PNormalize, PMagnitude, PDistance & PReflect, adding extrude-shell to PExtrudeable, adding subheadings for protocol impls

thi-ng/geom,JDReutt/geom,thi-ng/geom