Generating image data explicitly

• Restructured to generate the imagery all-at-once instead of using CGDataProviderCreateDirect().
	» This gives us the advantage of being able to optimize our loops better, generating shared data ahead of time rather than repeatedly.
	» Also gives us more-accurate profiling as we’re in charge of when most of the work (the image data generation) happens.
	» `genDestImageBytesAtPosition()` sorta became `createDestImageData()` and now handles `malloc`ing the whole image’s data and setting up data used by the generation algorthm, looping through every pixel calling `genDestImagePixelBytesAtPosition()`, and returning the new image data.
	• New `struct DestImageGenInfo` is created by `createDestImageData()` with all the info needed for every pixel, then used by each iteration of `genDestImagePixelBytesAtPosition()`.

Also:
• Renamed a few vars: `_destImageWidth`/`Height` to just `_destWidth`/`Height`, `_destImageTotalBytes` to `_destByteCount`.
• Set up a `kComponentCount` constant and used that in place of explicit `4` all over.
• Added `const`s to most of the functions’ args.
	» Started with defining a couple of things as `static const`s and went on from there.