add function 'shapeFromGLSL'

[Peter Whidden]

create an sdf primitive using sdf string

[Peter Whidden]

provide glsl source which defines a function which defines an sdf with signature 'float shapeSDF(vec3 p)'
automatically create primitive

let mySphere = glslShape(`
float shapeSDF(vec3 p) {
    return length(p) - 0.5;
}`);

mySphere()

[Torin Blankensmith]

It's working! de8e517