…o the hardware (particularly the extra map-mask bits in MAPL, MAPH)

This commit allows to set Xemu window position via CLI switch. Also, UI
menu has been added to be able to save current window position which is
restored on the next execution of the emulator. The save itself is NOT
automatic, since it seems, this is a bit awkward (not because of Xemu):
it seems sometimes SDL2 sees window pos _without_ the decoration border,
but sometimes with it ... So always saving winpos (window position) and
always restoring it can cause the window to draft away a bit at every
executuion, which is annoying ...

Mteufel pointed out another mistake in register dump. As-is fix
according to him.

Note: this is _not_ a proper fix, rather than a workaround by setting
CIA latched values to $0101 initially on start-up. Without this, newer
beta ROMs (v920391 and v920392) is left in an infinite loop at their
start-up routines with some CIA checking magic ... As a real MEGA65
works without workarounds, this must be an Xemu issue, but the proper
fix is hard to develop because the inprecise basic foundation of Xemu
for clock-accurate CIA emulation :( See the mentioned #395 issue above
for more details.

Plus a 'shade' command to set the transparency of the matrix background.

Note, currently I don't know why the slow device space is used for OPL
why not the native I/O space, or the MEGA65 specific OPL regs
at $FE000xx which is intended for that very purpose!

btoschi on Discord has great success to make OPL working on MEGA65 but
requires this access mode, so this quick hack is intended to serve that
holy purpose :)