Document Flash Slot Boot Selection Logic

[gardners]

The following information needs to be documented in the appropriate place:

MEGAFLASH starts

• D67E is read and saved early
• if MENU KEYS are not pressed proceed autoboot
• type of inserted cartridge is determined by checking saved D67E and cartridge memory signatures and is saved as the search flag
• if no cartridge was found search flag is set to DEFAULT
• core slot is searched that matches search flag
• if no slot is found, D69D is used to determine if slot 1 or 2 should be used
• only valid cores will be booted, otherwise FACTORY CORE proceeds or warning is displayed (depends on the type of invalidity)

fully backwards compatible. if you have no core flags set, your dip switch still works.

but as I said: there is no slot 1 that is automatically booted for every user out there. And it makes no sense to implement all if this in every tool we write.
Power cycling is no big deal and does what the user expects.

see also this issue: MEGA65/mega65-core#683