introduce Storage abstraction interfaces
use Storage i/f to load zip and 7z archives, cdi/cue/gdi/chd media,
cheats and to find custom textures.
Use android file picker to add storage. Request persisted access perms.
jni helper classes.
Issue #813
gd cart: load first .bin if the specified one isn't found. Fix loading
of main directory for mj1. Don't update progress too often when
decrypting.
chd: allow loading of 1-track CD-ROMs
Use 2 jvs boards for mj1
Issue #985
* cmake: use c++17
* Use std::size
* Use std::make_unique
* Use std::clamp
* Use structured binding
* Use [[fallthrough]]
* Use enable_if_t/is_enum_v/is_integral_v/is_same_v
* Use if constexpr
* Use try_emplace
* Use auto for iterators
* Use inline variables
Verify md5 of flash, eeprom, vmus if no savestate used
Use chd header SHA1 as digest
Load .state.net state file at start
Force real BIOS for some games
Pass LoadProgress object to report load progress and cancel
Better UI
Cancel with exception
Fix issues when stopping/exiting in !threaded
dx9: call gui_term on shutdown
Flyinghead