anduril build-doc should fail when no argument is given

[Kristian Ovaska]

When running anduril build-doc, it prints:

--api nor --html given. Not doing anything.

It should not accept an empty args list. It should fail by printing the usage message, and return 1.

[Ville Rantanen]

fix Issue #28

→ <<cset 73c8f76ff2b7>>