* Moved several machine lifecycle callbacks to the notifier/subscriber
model. The old callback registration model is still available for
them for now, but prints a deprecation warning.
* Added pre-save/post-load notifications.
* Use a single allocated timer rather than one anonymous timer per
waiter. Waiters no longer prevent saved states from being loaded.
* Clean up outstanding waiters on stop or state load rather than just
leaking them.
* Started documenting parts of the emulator interface object that should
be relatively stable.
-imagedev/avivideo.cpp: Fixed an object leak on unload. Also changed
some other media image devices to use smart pointers.
* Use the plugin data folder for storing the cache. The history folder
may be read-only or shared with different configurations.
* Don't create the cache database or surrounding folder if there's
nothing to store in it.
* Actually use prepared queries multiple times rather than always
destroying them after a single use.
* Added proper error checking for most database operations.
* Improved query performance by avoiding outer joins and table scans.
-bus/nubus: Made the Macintosh Display Cards map the blue channel to
white with monochrome monitors. Also added logging for PLL
configuration to help debug how CRTC and RAMDAC clocks work in the
future.
* bus/nubus: Started emulating SuperMac Spectrum/8 CRTC.
* bus/nubus: Respect Apple 4•8 screen base register.
* cpu/m68000: Fixed disassembly of bit field extract instructions.
* Also cleaned up data plugin a little.
