Rommable -- support other cell and mem sizes

[mitra42]

Following on from #60, Romable16_16 only supports Cell=2 mem=16 i.e. storing 16 bit cell in 16 bit memory.

It would be good to extend it - as for Mem{8,16,32}_{16,24,32} to support other combinations.

Once done, the Mem versions can be obsoleted.

Note - see also #64 about romsize=0

[mitra42]

Now supports Cell=4 mem=32 (suitable for ESP8266)

[mitra42]

Now supports Flash8_16, Flash8_24, Flash8_32, Flash16_16, Flash32_32 and Mem versions removed