Fix bug at modify interaction construction time

This fixes a bug that occurs when the modify interaction is configured with a non-empty collection of features.
Export ol.source.TileImage
Merge pull request #1972 from elemoine/modifyinteraction

Fix bug at modify interaction construction time
Merge pull request #1942 from elemoine/export-tileimage

Export ol.source.TileImage
Adding a JSDoc configuration for generating metadata on exported symbols

This generates info for all symbols annotated with "@todo api" (when Plovr is replaced, this will become "@api").  Generated metadata is written to stdout.  A separate process will handle the output.
Add a task to generate metadata on exported symbols

This runs JSDoc with the "symbols" config, providing a list of source files that have been changed since the previous run.  The output is used to generate metadata files containing exported symbol info for each of the source files.  A separate task will be run to generate the exports.js file.  These same metadata files will be used by a build tool.
Write a single symbols file
Add extends info to symbol metadata
Rename group to package
Annotations for geom exports
Annotations for format exports
Annotations for dom and events exports
Annotations for control exports
Annotations for assorted exports
Annotations for interaction exports
Annotations for layer exports
Annotations got proj exports
Annotations for immediate rendering exports
Annotations for source exports
Annotations for style exports