* Name change for consistency with other platforms: _system_bits -> _SYSTEM
* Add _SYSTEM extern to msx.h and sms.h
* Make all platforms have SYSTEM_60HZ and 0x00 and SYSTEM_50HZ as 0x01
* Make _SYSTEM have uint8_t type instead of UBYTE
* Add new zeropage variable _system_bits to indicate NTSC/PAL/Dendy system
* Modify init code to detect NTSC/PAL/Dendy via cycle counting, storing result in _system_bits
* Modify fake-LCD-ISR delays in NMI handler to accommodate PAL timings
Cross-platform:
* Change existing SYSTEM_NTSC / SYSTEM_PAL defines in sms.h to SYSTEM_60HZ / SYSTEM_50HZ, and copy them to gb.h / nes.h / msx.h
* Add new cross-platform function get_system for all ports, to query whether running on a 60Hz or 50Hz system
* Add minimal cross-platform display_system example to exercise get_system
* Update gbdk-lib/include/gb/gb.h to forward set_bkg_native_data / set_sprite_native_data to set_bkg_data / set_sprite_data functions
* Update gbdk-lib/include/sms/sms.h to forward set_bkg_native_data / set_sprite_data to set_bkg_4bpp_data / set_sprite_4bpp_data
* Add implementation for set_bkg_native_data / set_sprite_native_data in gbdk-lib/libc/targets/mos6502/nes/set_native_data.s
* Update gbdk-lib/include/nes/nes.h to include function declarations for set_bkg_native_data / set_sprite_native_data
* Update gbdk-lib/inlcude/nes/nes.h to implement set_native_tile_data in terms of set_bkg_native_data / set_sprite_native_data
* Update gbdk-lib/inlcude/nes/nes.h to implement set_tile_data in terms of set_bkg_data / set_sprite_data
* Remove old (/broken for indirect mode) code for set_tile_data / set_native_tile_data from set_data.s / set_native_data.s
* Update png2asset to include NES among the supported PackModes
* Update examples/cross-platform/logo .meta file to specify NES PackFormat for NES build
* Update examples/cross-platform/large_map Makefile to specify NES PackFormat for NES build
* Add dedicated NES function set_bkg_attribute_xy_nes16x16 for setting an individual (shadow) attribute in gbdk-lib/libc/targets/mos6502/nes/set_attribute.s
* Add inline adapter NES function set_bkg_attribute_xy, which calls set_bkg_attribute_xy_nes16x16
* Change NES functionality to call _flush_shadow_attributes from wait_vbl_done
* Remove calls to _flush_shadow_attributes in set_bkg_attributes and set_bkg_submap_attributes
* Add dedicated SMS/GG function set_attribute_xy in gbdk-lib/libc/targets/z80/set_tile.s
* Add inline adapter GBC function set_bkg_attribute_xy in gbdk-lib/include/gb/gb.h
- more details for for new metasprite functions
- GB: more details for BGP/OBP0/OBP1
- Remove some trailing spaces in metasprite headers
- Re-add Obsolete keyword to pre-deprecated functions
- Entries for release notes, migration notes
- Add note about initializing SRAM
- Add CGB section to Supported Consoles with overview, api links and list of examples (@anchor using_cgb_features)
- Initial note 4.2 migration and release notes
- API doc improvements
* Add wrapper functions set_bkg_attributes / set_bkg_submap_attributes to sms.h
* Update png2asset to always output a #define that makes attribute map equal tile map when attributes are not generated
* Update examples/cross-platform/logo to use set_bkg_attributes unconditionally
* Change sms_metasprites to have 4 permutations for flipping combinations, using a generic macro for function bodies
* Change examples/cross-platform/metasprites to duplicate uploaded tiles by X and Y depending on HARDWARE_SPRITE_CAN_FLIP_X/Y defines
* Change examples/cross-platform/metasprites to use 8x8 sprites, to make all duplicated tiles fit tile memory on sms/gg
* Remove hide / show metasprite functionality in examples/cross-platform/metasprites
* Move rotation to A button, to make compatible with 2-button SMS joypad
* Update printing of METASPR_ITEM in png2asset to extract X/Y flip and palette number, print them as symbolic names S_FLIPX, S_FLIPY and S_PAL(...)
* (...and adjust output formatting to one METASPR_ITEM per line, for better readability)
* Add #define for S_PAL to gb.h, nes.h, msx.h and sms.h
* Remove "TODO:" comments from gbdk-lib/libc/targets/mos6502/nes/metasprites.s
* Add metasprite variants move_metasprite_hflip, move_metasprite_vflip and move_metasprite_hvflip to gbdk-lib/libc/targets/mos6502/nes/metasprites.s
* Add HARDWARE_SPRITE_CAN_FLIP_H / HARDWARE_SPRITE_CAN_FLIP_V defines to nes.h / gb.h / sms.h / sms.h, to allow cross-platform info on HW sprite flip support
* Update examples/cross-platform/metasprites/src/metasprites.c to use flipped metasprites when available on platform
* Delete old gb-specific examples/gb/metasprites, in favor of cross-platform version
