Adding simple measure example
Add ol.source.TileWMS#getUrls
Add ol.source.ImageWMS#getUrl
Replace typedefs with externs

Since the compiler leaves externs untouched and learns the used
properties from object literals, this replaces the otherwise
required typedefs just fine.
Merge pull request #1971 from ahocevar/externs-instead-of-typedefs

"Cannot read property 'AttributionOptions' of undefined" error
Add a comment to build.py
Merge pull request #1977 from elemoine/comment

Add an olx.js related comment to build.py
Merge pull request #1950 from jachym/measure_example

Adding simple measure example
Add file propery to ol.interaction.DragAndDropEvent
Remove undefined type from opt_target and opt_file
Merge pull request #1982 from fredj/dnd-event

Add file propery to ol.interaction.DragAndDropEvent
Allow '{-y}' placeholder
Merge pull request #1983 from fredj/osgeo-url

Allow '{-y}' placeholder
Merge pull request #1970 from elemoine/geturls

Add getUrl methods to TileWMS and ImageWMS
snapshot