PHLEGM v8 firmware cache for PET-2001NT

No ROM binaries are shipped by PHLEGM.
Slots, addresses, byte lengths, CRC32 checksums and download URLs are in firmware.config.phlegm.
With Networking enabled, missing firmware is fetched and verified before machine startup.
Hardware profile: Teacher's PET 2001NT, 32 KiB normal/graphics-keyboard BASIC 4 configuration; 40x25 TTL, no CRTC. Actual Teacher edition ROM revision may differ.
RAM address range: $0000-$7FFF; memory size: 32 KiB.
Firmware slots: 6
