PROGMEM support?

Created by: brunnels

I'm pretty low on memory in one of my projects so I'm trying to scrape a few bytes together by moving strings into PROGMEM. Would it be possible to add support for this or should it work and I'm doing it wrong?

// normal way
root["relays"].as<uint8_t>();
// using PROGMEM macro that doesn't work but does compile
root[(const char*)F("relays")].as<uint8_t>();