datomic-free on npm

I wrapped your project with node.js / package.json (with the help of [bon](https://github.com/orlin/bon)) and published it to [npm](https://www.npmjs.org/package/datomic-free) mostly because I want to use it for testing [datomiki](https://github.com/datomicon/datomiki) (or other datomic projects) and have it as a dependency.  It also puts itself in the path thanks to [install-g](https://github.com/orlin/install-g) that I just wrote.

Also changed the [readme](https://github.com/datomicon/datomic-free#description) a bit to reflect the new install option, also check the usage tweaks.  We should perhaps publish it with a version to match the latest tagged release - assuming master always contains released code and work is to be done in other branches.  Otherwise I could reference a github tag from package.json, I guess that is the best way to go anyway.

I fork the repo automatically, but don't check it or pull.  The `bin/datomic-free` comes with `npm install datomic-free`.  It can be upgraded with npm again.  Right now I don't see a reason to pull after the initial clone.  We could install other files with npm as well...