Add `@todo observable` documentation for observable properties

This PR adds documentation for observable properties, which will then be pulled into the docs correctly once #1180 is merged.  This is a first pass based on searching for definition of observable properties being defined as enums after lines ending with `Property = {`.  If there are observable properties implemented that don't follow this pattern then they are not included.

I've added simple descriptions based on what I know or could easily figure out, there may be some properties (like preload) that are not correctly described.

I've also added `readonly` annotations where I knew that a property was readonly.  I may have missed some readonly properties.

ol.layer.Base has a bunch of properties but I don't think it is exported so the documentation of these properties will not show up, so I added the documentation to ol.layer.Layer instead even though this isn't really where it should be documented.
Add ol.coordinate.format function

Return a formatted coordinate. Example usage:
  > ol.coordinate.format([0.01 ,12.14], "{x}, {y}", 2)
  "0.01, 12.14"
  > ol.coordinate.format([0.01 ,12.14], "lat: {y} / lon: {x}", 1)
  "lat: 12.1 / lon: 0.0"
Remove opt_precision check in ol.coordinate.format

Default is already 0, see http://www.ecma-international.org/ecma-262/5.1/#sec-15.7.4.5
Better ol.coordinate.* documentation
Fix `@todo observable` name reference.
Remove unnecessary Get column from observables
Quote values in apidoc
Fix bottom left and top right computation in moveend example
Merge branch 'master' of https://github.com/openlayers/ol3