PHLEGM v8 firmware cache for PET-2001-8B

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: BASIC 2, business keyboard, 40x25 TTL, no CRTC; revised PET board; not original chiclet-keyboard Japanese 8B variant.
RAM address range: $0000-$1FFF; memory size: 8 KiB.
Firmware slots: 5
