Change sourceDir to src/ in generate-info.js

This is to accomodate the case where other directories than "ol" include "api" annotations. For example, the Swisstopo geoadmin folks extend OpenLayers 3 in an ol3 fork, and they have their own "ga" namespace/directory under "src". See https://github.com/geoadmin/ol3/tree/master/src.
Remove ol.easing.elastic and ol.easing.bounce

And move the code to the animation example
Merge pull request #2188 from fredj/easing

Remove ol.easing.elastic and ol.easing.bounce
Mark abstract method as function for JSDoc to pick it up

This leaves aside the question whether getImage needs to be
defined as abstract method in a base class that does not know
about images, but at least it makes the documentation appear
correctly in ol.tile.Image.
Merge pull request #2191 from ahocevar/tile-function-annotation

Mark abstract method as function for JSDoc to pick it up
Merge pull request #2174 from elemoine/generate-info

Change sourceDir to src/ in generate-info.js
Update closure-util

The closure-util package works on Node 0.8, 0.10, and 0.11 (as of this writing), but it requires an updated version of npm to install on Node 0.8.  For the build to pass on Travis, we update npm before installing other dependencies.  For others who are installing the openlayers package, nothing special is required for Node 0.10 and above.  For users on Node 0.8, the openlayers package will only install with an updated version of npm.  This can be installed with npm itself.

    npm install -g npm # only needed on Node 0.8
Merge pull request #2197 from tschaub/deps

Update closure-util.
Add standard docs text to abstract base classes
Merge pull request #2199 from probins/abstract

Add standard docs text to abstract base classes