=== Simple Image Format ===

U16	Magic	0x51F0	- This determines the endianness of the file
U16	Flags
	> 0-2: Compression (0: Uncompressed, 1: RLE, 2: zlib, 3: RLE-Channel)
	> 3-5: Format (0: ARGB, 1: RGB
U16	Width
U16	Height
<DATA>


=== Compression Formats ===
0 - Uncompressed
	The file data is a linear sequence of Width * Height 32-bit ARGB
	words (in file endianness, determined by the magic)

1 - RLE-4
	7-bit length followed by a 32-bit value that is repeated `n` times
	(if bit 7 of the length byte is set, the next `n` 32-bit words are
	verbatim)

2 - zlib
	The image data is a zlib stream of 32-bit xRGB words

3 - RLE-Channel
	The data is the alpha values, followed by red, then green, then blue
	encoded as RLE with a 7-bit length and a verbatim flag (same as mode
	1, except with 8-bit values instead of 32-bit)