PHLEGM v8 firmware cache for CBM-4004-N

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: CBM 4004 nominal 4 KiB, BASIC 4.0, normal/graphics keyboard, 40x25 TTL (pre-CRTC 9-inch board).
RAM address range: $0000-$0FFF; memory size: 4 KiB.
Firmware slots: 6
