Avoid protocol relative URL to support apps using file protocol
Use native JSON.parse function
Remove undocumented symbols at the end of the parsing process

This ensures that we do not mark symbols as undocumented before
all potential dependencies are parsed.
Only add symbols to the unexported array once

This basically fixes a typo that caused unexported symbols to
be added to the unexported array multiple times.
Also consider linked symbols as documented
Make ol.render.canvas.Immediate available in the docs
Make ol.View2D available when exploring olx.MapOptions
Do not query the array twice
Merge pull request #1904 from ahocevar/doc-improvements

API doc improvements
Do not delete event and fires doclets
Do not loop through parents

Now that we use the parseComplete event, we walk through all
doclets in the loop anyway.
Take the feature's weight into account
Add new 'weight' option to ol.layer.Heatmap
Clamp opacity value to (0, 1)
Better documentation for weight option
Merge pull request #1902 from fredj/native-json

Use native JSON.parse function
Remove unneeded json.js extern
Merge pull request #1909 from fredj/extern

Remove unneeded json.js extern
Clean up

Only mark symbol as unexported when it is not in the API, and
no longer extract links from fires annotations because all links
are handled now.
Use a more visually appealing margin for descriptions