Merge pull request #21 from zqsd/develop

HDR environment map example
Add prefix feature
Merge branch 'develop' of github.com:cedricpinson/osgjs into develop
Merge pull request #22 from zqsd/develop

HDR and Cubemap examples improvements.
Merge branch 'develop' of github.com:cedricpinson/osgjs into develop
Add extra parameters to extend object
osg.performance.now fallback of performance.now