Use externs/olx.js instead of objectliterals.jsdoc

The single externs/olx.js file describes all of the "options" objects we accept in our constructors.  The @typedef annotations are used by the compiler for type checking.  The @type annotations include documentation for individual options and serve as externs when compiling a profile of the library.  When compiling an application together with the library, the externs/olx.js file is included as one of the sources to provide the @typedef's without generating externs.

If we want to maintain multiple src/*.externs.js files instead of one large externs/olx.js file, we can.  But while we are still using Plovr, it makes for easier build configurations to have one file.

This removes the build tasks that generated the build/src/external/src/externs/types.js and build/src/internal/src/types.js files as those are both replaced by the single externs/olx.js file.
Unused externs and typedef generating code
Parse olx.js and convert types into typedef properties
Adding comment about using externs/olx.js as a source file

The externs/olx.js script includes @typedef annotations for objects that are used in the library.  When compiling the examples together with the library, we need these @typedef annotations.  In this same case, we don't need the object property names to be treated as externs (they can be safely renamed).
Merge pull request #1954 from tschaub/olx

Use externs/olx.js instead of objectliterals.jsdoc.
Don't use 'this' keyword in tileUrlFunction

See a31ad69ec4c0cf530a5f52aad9ada649ea390204
Fixes #1965
Use WMTS server from services.arcgisonline.com
Merge pull request #1967 from fredj/tileUrlFunction-this

Don't use 'this' keyword in tileUrlFunction
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