since there isn't another "layer" to replace the masked pixels with, there's an option to replace them with either a fixed color or a color from 32X palette RAM
* new option to darken Genesis colors relative to 32X colors, since the brightest 32X colors are brighter than the brightest Genesis colors on actual hardware
* new yellow/purple color tint options that attempt to simulate how 32X colors look on actual hardware, though the exact effect seems to vary between consoles
the biggest changes, at a high level:
* created new crates smsgg-config, genesis-config, nes-config, snes-config, gb-config that contain structs/enums serialized into the config file (these were previously all in the respective backend crates)
* flipped the dependency between jgenesis-native-driver and jgenesis-native-config - the former now depends on the latter rather than vice versa
* jgenesis-native-config no longer depends on any backend crates, only the config crates and jgenesis-renderer
these changes prevent Cargo from needing to recompile any crates with heavy use of serde derive macros when there are only changes to one of the backend cores
this should also _slightly_ help with initial compile times since jgenesis-native-config no longer depends on any of the backend crates, which should allow for slightly greater parallelization
