option detection

Right now i tried ```mbed new -mbedlib .``` with the intention to use os2,
but the outcoming shows, it is os5 as a file mbed-os.lib is created with the according link.
I just typed ```-mbedlib``` instead of ```--mbedlib```.

I would expect an error telling me that the option is unknown.
I suspect, this is a quite general bug not specific to the command ```new```.

Reproduce `mbed new -mbedlib .` and inspect the mbed CLI option parsing used by `new`, then check whether the same behavior occurs in other commands. Done means an unrecognized single-dash option reports an error and does not create or select `mbed-os.lib`; add regression coverage for the rejected option.

Written by the indexing model from the issue text.