Support zoom and resolution constrained views

This adds support for `minZoom` and `minResolution` options (in addition to the existing `maxZoom` and `maxResolution`).  Where both `minZoom` and `maxResolution` are provided, `maxResolution` is given precedence.  Where both `maxZoom` and `minResolution` are provided, `minResolution` is given precedence.

Fixes #1168.