paged 1 MB SRAM/512K flash

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A respin of the RC2014 ecosystem. I don't have any opposition to building things out of SMD parts (in some ways, I find it easier to work with), so some boards might go that way to the extent that parts availability allows. Also, I'd like to keep all board sizes within the 100x100mm limit within which PCB fabs offer their cheapest rates (like $2 double-sided at JLCPCB, for instance).

This started out as a copy of the schematic from the RC2014 GitHub. I brought it into KiCad 6, replaced the "rescued" symbols from the original with more current ones in the KiCad library, redid the connections in what I think is an easier-to-follow style (global labels instead of buses), and re-did the PCB layout from scratch (since that wasn't included). I also swapped out SMDs for through-hole parts.

This freed up enough space to add a second SRAM chip. Banks 0-31 select ROM (flash) and banks 32-95 (previously 32-63) select RAM. 16K chunks of either ROM or RAM can be paged into any of four slots in the memory map: $0000-$3FFF, $4000-$7FFF, $8000-$BFFF, $C000-$FFFF. Reset maps ROM page 0 into all slots.