add a bower.json to publish this as a Bower package

Bower is a package manager for the web. It makes installing front end libraries extremely easy:
`bower install roslibjs`

I created a bower.json with meta data such that bower knows about the dependencies of roslibjs. You can try this out by running the following command, it will install both roslibjs and EventEmitter2.
`bower install Rayman/roslibjs#develop`

In issue #80 we discussed this and concluded that bower needs a master branch. Now that we have a master branch, the bower.json can be integrated. I put the version at 0.9.0 so that it can be included in the next release.