Arguments of make_block_pulse are highly confusing

[wtclarke]

bandwidth, the second listed argument (default=0) has no effect (see relevant logic), unless the the default to duration (default = 4E-3) is overwritten by the user. This isn't documented anywhere, no warning is issued, and duration is listed several places below bandwidth in the list of arguments.

[sravan953]

Thanks for this, @wtclarke ! Would you be interested in submitting a PR wherein a warning is raised?

[wtclarke]

Done in #151 . I've also added markers for the tests, so only the tests we expect to work will run.

[wtclarke]

Closed in #151