Proposed, and implemented, some enhancements (1Mb + 1Mb firmware, resizable jsvars size, ...)

@Pedro

It'd be worth checking that the firmware update over WiFi can still function in the 1MB/1MB config

Here is the code for the over the air updates... there is a flash map address look up:
https://github.com/espruino/Espruino/blob/6da2ddd05917d98e0693a084a2d64fcfb8b800d1/libs/network/esp8266/ota.c#L171