The maximum number of cmdfunc names is 20, which IMO is too low. Worse,
if it's longer, nothing will warn us because C will just fill the array
to it's end (without \0 at the end). To remedy this:

- Allow longer names till 64 bytes (I hit the previous limit of 20)
- Check that the name is within the length limit: if somebody wants a
  very long name, the strnlen() will return the maximum length, hitting
  that assertion.
- When reading a command during runtime, allow the corresponding maximum
  length.

On that occasion, also increase total number of permitted cmdfuncs.