Add smscolours utility, along with Game Gear colours

Start refactoring code to rename and export various functions toward

go mod: update Go version and packages

Example splash.asm minor cleanup

Update README

Save tile data as PNG, update CLI for new flag

Update example readme

Better error when tile memory full

Add splash screen example and build script for ROM image

Improve Assembly output

Convert tile bytes to correct planar data

README usage instructions

Assembly output

Tile Bytes returns SMS formatted bytes

Output Tilemap data as SMS 16-bit WORDs