This commit updates the doc-gen to account
for the changes to the codebase for decorators.
There are actually three kinds of calls that create decorators:
* makeDecorator
* makePropDecorator
* makeParamDecorator
Also, the actual documentation for each
decorator is split between two exported symbols:
* `interface [DecoratorName]` contains the metadata fields
* interface [DecoratorName]Decorator` contains a
"call member" which holds the general description of the decorator.
This processor now identifies all three decorator types, and pulls the
description of the callMember onto the main decorator doc description.
(There are some outstanding interfaces in the angular/angular project that
need to be re-exported from `/angular/modules/@angular/core/src/metadata.ts`
to ensure that the doc-gen is able to access them.)
Closes https://github.com/angular/angular.io/pull/2349
Pete Bacon Darwin