Implement ZX Spectrum 48K

[vbmacher]

ZX Spectrum48K basic info: https://worldofspectrum.org/faq/reference/48kreference.htm

ZX Spectrum tests:

• https://github.com/raxoft/z80test
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/timing_tests-48k_v1.0.tzx
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/timing_tests-128k_v1.0.z80
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/softspectrum_48_2019-03-08_21-29-34.mp4
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/fusetest.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/floatspy.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/minfo.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/btime.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/stime.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/ulatest3.tap
• https://softspectrum48.weebly.com/uploads/6/6/7/5/66753101/ptime.tap
• https://github.com/MrKWatkins/ZXSpectrumNextTests/tree/develop/Tests/ZX48_ZX128/Z80BlockInstructionFlags
• https://softspectrum48.weebly.com/test-results.html
• https://spectrumcomputing.co.uk/forums/viewtopic.php?p=94582
• https://skoolkid.github.io/rom/maps/all.html

[vbmacher]

Leftovers:

Keyboard

The mapping of all ZX keys to host keyboard is implemented correctly. Additional TODO is to map additional host keys, like backspace or delete for increased user experience.

The visual keyboard shown at the bottom should recognize "graphics" mode and change keys images accordingly. Also, if SHIFT / CTRL is pressed, the shift/symshift should be filled with different color.

Contention

Memory + I/O contention should be implemented properly

Documentation

ZX Spectrum documentation should be started in the website. The documentation should include all Z-80 tests which pass or don't pass.

Audio tape player/recorder

TODO is to suppot TZX files, and possibility to save recordings to TAP/TZX files.

Audio

Audio output should be implemented.