Merge pull request #92 from twpayne/request-render-frame

Request render frame
More strict matrix type
Remove inadvertent double render
Avoid getting map twice
Factor out color matrix generation, move color matrix into layer renderer
Merge pull request #93 from twpayne/webgl-renderer-cleanups

WebGL renderer cleanups
Disable document generation in precommit target, refs #94

Revert this commit when issue #94 is fixed.
Correct Stamen source options
Snapshot