Image Capture spec: new version

Hi All,
I'm enclosing a new version of the spec.  Thought I'd circulate it before updating the GH repo.  Major changes:

a) Added flash and focus settings.  I derived these settings from https://dvcs.w3.org/hg/dap/raw-file/tip/media-stream-capture/proposals/SettingsAPI_proposal_v6.html, which reflected what was once consensus within the group.

b) Got rid of all event handlers.  All asynch methods are now promises.

c) Kept 'zoom' as an unsigned long, but am willing to change this.  Wanted to get more feedback about the data types for other numeric settings, rather than addressing piecemeal.

d) Changed ImageCaptureError so that it does not provide numeric codes.

e) There is are two open questions on grabFrame():  i. Should it return an ImageData or Image Bitmap object? Ii. Should photo settings be applied to the captured frame?
 I've added text that allows for photo settings to be applied in the execution of grabFrame(), but I would really like implementor feedback.  My initial feeling is that if the photo settings are not applicable to grabFrame() then the method does not provide more value than Example 2 in http://www.w3.org/TR/mediacapture-streams/ (i.e. the old snapshot example in the gUM spec).