#2 Allow custom functions

[Anonymous]

Allow variable definition on the fly in expressions
like:
r:sqrt(x^2+y^2);
sin(r)/r

or even:

sin(r:sqrt(x^2+y^2))/r

Allow custom function definition on the fly in
expressons like:

r(a,b):sqrt(a^2+b^2);
sin(r(x,y))/r(x,y)