More general solution to skip N[0-9]+[ ]* in the parser as in #2218

- When editing on the LCD, minus now means below the nozzle
- Stores the opposite sign in EEPROM, so bumped to “V20”

For sprintf_P() the first parameter has to be a `char*` not `const char*`.

replace extruder_multiply with extruder_multiplier
like feedrate_multiplier or volumetric_multiplier

- Use `setTargetedHotend` in `M200`, as with other commands that use
`T` for the extruder
- Synthesize the "invalid extruder" message, obviating several long
strings

Was omitted when T0 is a MAX6675.

to have it ready to display errors during (temperature)-setup.

- The command parser now displays “unknown command” in more cases.
Known commands must be added to the `switch` inside `process_commands`
to suppress the error.

- Affects code size when automatic bed leveling is enabled

Makes the output on the LCD adjustable.

- Use a global pointer for the current sanitized command
- Pre-sanitize the current command to bypass `N` and nullify `*`,
removing the need for handlers to bypass, ignore, or nullify these
parts, and reducing overhead for `code_seen`, etc.
- Pre-skip leading whitespace.
- Only look for G, M, T codes at the start of the command.
- Verify that G, M, T codes are followed by command codes.