Add Polymer.version

[ebidel]

Lots of libraries do this and it's pretty handy to be able to quickly check what release version of Polymer is being run in an app. Adding a .version property on our global object would be ace.

Similarly, build files should include an @version string. See #226

[dfreedm]

I should be able to handle this for the next stable revision

[addyosmani]

@azakus in #226, the @Version was added to builds in a comment form, but I'm unsure if Polymer supports .version. as yet. Has this already been solved or are there plans to get this in soonish? :)

[dfreedm]

The .version property has been low priority for me, but I can probably make it go by the next release.

[twistedpair]

I've added Polymer to the Library Detector for Chrome (pull request pending) but can't display the version because Polymer doesn't have a .version property. Please add this so folks can easily see what version is running. Since the version is already being inserted into the source headers, this should be a pretty simple addition to make. Thanks.

[twistedpair]

Thanks @azakus!