Add --color-field for per-value highlighting

[omdxp]

Adds a new CLI option to colorize object string values based on key=value rules, intended for structured log fields like level. Includes docs updates, a manpage regen, and tests.

[omdxp]

What this adds

New CLI flag: --color-field key=value:SGR
It forces a specific ANSI color for matching string values (by key + exact value), on top of jq’s normal -C coloring.

Example (realistic app logs)

Input (NDJSON):

{"time":"2025-12-16T23:11:01Z","level":"debug","msg":"starting server"}
{"time":"2025-12-16T23:11:02Z","level":"info","msg":"request","status":200}
{"time":"2025-12-16T23:11:03Z","level":"warn","msg":"slow query","duration_ms":842}
{"time":"2025-12-16T23:11:04Z","level":"error","msg":"upstream timeout","attempt":3}

Command:

jq -c \
  --color-field 'level=debug:0;36' \
  --color-field 'level=info:0;32' \
  --color-field 'level=warn:1;33' \
  --color-field 'level=error:1;31' \
  '.'

Expected terminal appearance (approx):

• DEBUG: "debug" (cyan)
• INFO: "info" (green)
• WARN: "warn" (yellow)
• ERROR: "error" (red)

Raw ANSI proof (same output, escape bytes visible):

• debug: \x1b[0;36m"debug"\x1b[0m
• info: \x1b[0;32m"info"\x1b[0m
• warn: \x1b[1;33m"warn"\x1b[0m
• error: \x1b[1;31m"error"\x1b[0m

Notes

• --color-field implies -C (so it still works when piped).
• -M overrides and disables all color output.