Implement remote archive basic authentication

[Knetic]

#20 will support remote unauthenticated archive fetching, but it's still desirable in some cases to have authenticated remote archives be used.

If a remote archive is requested (either through -a or as the first positional) from an authenticated source, stdin should be used to receive first a username then password, which is then used to try to auth. If auth fails, wisk should quit with a non-zero exit code.

Additionally, the user should be able to specify --user and --pass flags, which are used as the username and password instead of stdin input. If --user is not specified, stdin should be used as if the flags did not contain a --pass.

[Knetic]

Done as of c155df6