Add NC 700 support, logging, and CMake build

[JohnMansell]

Note: This contribution was developed with AI assistance (Claude by Anthropic).

Issue

The NC 700 was not recognised by the tool and the protocol handling assumed fixed-size responses, which broke on devices that return different payload lengths. Most set commands on the NC 700 do not send a confirmation packet, causing the tool to report failure even when the setting was applied. The original read() calls did not retry on short reads, making them fragile over RFCOMM. There was no way to inspect raw packet traffic when debugging a new device.

Solution

Add explicit NC 700 support and harden the protocol layer to handle variable-length, length-prefixed responses. Treat EAGAIN on a confirmation read as success for devices that do not send one. Loop inside read() until exactly N bytes are received. Add a leveled logging system so packet-level traces can be enabled on demand without recompiling.

Changes

• based.h: add DeviceId enum (QC35, QC35_II, SOUNDLINK_II, NC700); expand VER_STR_LEN from 6 to 32; fix send_packet parameter name typo.
• based.c: add DEVICE_NC700 to has_noise_cancelling(); add read_exact() helper that retries short reads; refactor init_connection, get_device_id, get_firmware_version, and get_battery_level to read a 4-byte header and drain a length-prefixed payload; handle EAGAIN-as-success in all set commands; fix get_name mask to accept NC 700 encoding byte; simplify set_voice_prompts to not fetch full device status first; replace abs() difference comparisons with != for enum return values.
• main.c: add -D / --debug flag wired to log_set_level(LOG_LEVEL_DEBUG); increase SO_RCVTIMEO from 1 s to 5 s; fix receive typo; improve error reporting when a command returns non-zero.
• log.c / log.h: new leveled logging module (DEBUG/INFO/WARN/ERROR), off by default, writes to stderr with file/line/function prefix and a hex-dump helper for packet bytes.
• CMakeLists.txt: new CMake build (C11, -Wall -Wextra -Wpedantic).
• COMPATIBILITY.md: per-device feature matrix and per-device protocol notes covering QC35, SoundLink II, and NC 700.
• README.txt: document -D flag, update disclaimer, expand todo list, add contributing / adding device support guide with HCI capture instructions.

[zewelor]

Confirmed on my NC 700 FW 1.8.2