[Bf-python] Mathutils additions

[Anders Nilsson]

Area of triangle (pseudo-code)

Vector edge1=p1-p0 (vector subtraction)
Vector edge2=p2-p0
Vector temp=edge1.crossProduct(edge2)
float  area=getVectorLength(temp)/2.0

Anders Nilsson (breakin)

ps. Mail if you need the derivation of the "formula"