LayoutOptions to control allocations. about gamut

[p0nce]

Mmmm we can store that as flags into the Image, in order to stay self-contained:
So it is 2 bits for extra "gap" pixels, 2 bits for multiplicity, and 3 for scanline alignment.
The only flag combination that ensures to be gapless is 0.

[p0nce]

Basically we can use whatever the decoder can already provide as automatic conversion (for example, stb_image can force to 1/2/3/4 channels and do 8-bit/10-bit conversion at the row level), and then support other flags with convertTo, which is itself trained to see cases that needs nothing to do.

What we cannot do for now is force "gapless" contraint.

[p0nce]

• QOI and QOIX loader can be more efficient when decoding 3 channels to rgba8, or 4 channels to rgb8
• and QOI-plane can decode 1 to 2 and 2 to 1
• in conversion, intermediate buffer should be stuffed in the bonusBytes
• Force 8-bit, 16-bit, and 32-bit float loading with new LOAD_xxx flags. Though, only the PNG decoder will take advantage of this.
• isGapless() function. A function to get all pixels in an ubyte[]
• getters for various layout things

[p0nce]

Basically works.