Overhauled resend handling to also work with alwaysSendChecksum feature. Also introduced new feature flag resetLineNumbersWithPrefixedN to make M110 commands send the target line number as part of their N prefix (Repetier), not as a separate N parameter (Marlin & co)
Added known error messages for checksum mismatches or expected line issues from Repetier to recognized "auto-correction" errors, made code around all that a bit more readable.