Use new generate-exports.js task
Regenerate symbols if parents have changed

The generate-symbols.js task runs JSDoc on source files.  Because this takes a long time (13s) to run on the whole library, the resulting symbols file includes additional metadata to make it possible to do incremental symbol generation on subsequent runs.  The 'path' and 'extends' metadata for a symbol are used to determine what needs to be regenerated.
Call generate-symbols.js from build.py
Unused script
Generate symbols before exports
Build task for driving the compiler
Parse options and add docs
Accept a src config, add docs
Use symbols.json for determining the API

Also to get rid of regular expression parsing, instead of
collecting exports for observables from the source files, we use
the 'observable' annotations.
Include symbols from oli.js using interface and implements tags

Instead of regex parsing, we define tags for interface and
implements.
Greatly simplify and document the usage of JSDoc

This commit simplifies the exports.js plugin so it only relies
on the stability notes to generate the documentation, which
completely decouples it from the exportable API.

As a rule of thumb, whenever something has an 'api' annotation,
it should also have a 'stability' annotation. A more verbose
documentation of ol3 specific annotation usage is available in
the new 'apidoc/readme.md' file.

This commit also modifies all source files to implement these
usage suggestions.
Document purpose and use of oli.js and olx.js
Inline object literals from olx.js
Get rid of stability annotations and document stability with api

This change adds a stability value to the api annotation, with
'experimental' as default value.

enum, typedef and event annotations are never exportable, but
api annotations are needed there to make them appear in the
docs.

Nested typedefs are no longer inlined recursively, because the
resulting tables get too wide with the current template.
Exclude enums, events and typedefs in one central place
Fixes suggested by @probins
Allow configuration of JVM arguments in build
Accept a path for exports file