smarter object definitions

[ntessore]

This PR allows for a more straightforward definition of objects. Take a look at the new SIS lens:

// singular isothermal sphere
// follows Schneider, Kochanek, Wambsganss (2006)

type = LENS;

params
{
    { "x" },
    { "y" },
    { "r" }
};

data
{
    float2 x; // lens position
    float r;  // Einstein radius
};

static float2 deflection(constant data* this, float2 x)
{
    // SIS deflection
    return this->r*normalize(x - this->x);
}

static void set(global data* this, float x, float y, float r)
{
    // lens position
    this->x = (float2)(x, y);

    // Einstein radius
    this->r = r;
}

The following changes have been introduced:

• Objects live in the objects folder, to separate them from the main kernels.
• The name of the object need not be repeated inside the definition, for a more object-oriented feel.
• Separate functions for deflection and brightness (necessary for Mass follows light source / lens #101).

[ntessore]

This variadic macro is not actually supported by the OpenCL standard. However, it works in Apple's implementation. We must check whether this is true also for other implementations before we can merge this.

[ntessore]

I have marked this work in progress for now.

[ntessore]

This is ready for merging now. There is no longer any use of non-standard variadic macros, and the overall style is much nicer, I think.