Add additional debug logging for palette assignment #115
Description
Users are justifiably concerned that when palette assignment fails, the reasons are extremely opaque. There are probably some logs we can add so that --verbose mode provides additional insights to help folks debug their tilesets.
An idea: modify the ColorSets type so that it can store additional metadata about its source. Then logs can display actual source tile information when a ColorSet is unassignable (or in other relevant situations)