Convert between hex and text

Turn text into a hex dump with the separator you prefer — plain, spaced, colon-separated or 0x-prefixed — and turn any of those back into text. Decoding accepts whatever separators your source used, and when it cannot proceed it says why: characters that are not hex digits, an odd number of digits, or bytes that are simply not text. Partial output from a broken dump would look like data, so you never get it.