Clarify BBOX format

[cholmes]

From @jjrom: 'The format of bbox is unclear from the specification. The astrea implementation waits for a comma separated delimiter string (i.e. lon1,lat1,lon2,lat2) while the Element84 implementation waits for an array i.e. ([lon1,lat1,lon2,lat2])'

He found that Features API is without an array, since we aiming to fully align with that I think we should use that, and make it clear.

[jisantuc]

fwiw Franklin also assumes no array brackets for bboxes in query params

[jjrom]

Same for https://github.com/jjrom/resto - it also assumes no array brackes for bboxes in query params

[cholmes]

Am making a PR for this and it seems pretty clear. Will put in a few more warnings, but I think we mostly need to get @matthewhanson to update the element84 service.