PSTR() and F() macros correctly place string into flash memory relying
on PROGMEM
PROGMEM uses ICACHE_RODATA_ATTR
Print and String classes fixed up
str* classes fixed up
This includes empty stubs for most core Arduino functions.
Need to actually implement all those digital reads writes whatever.
Need to prebuild toolchains (xtensa-elf-lx106) for 3 platforms and put them on some download server.
Need to do the same with esptool.
Need to fix 0x40000 binary generation and add correct upload commands.
Maybe even implement uploads over WiFi.
