Added VERSION and updated setup to read it.

Progress on #1447.
@oxtopus Do you know how I can get the version available from inside the python runtime without this line?

```
import nupic
nupic.__version__
```

Is there any way to do this from within setuptools? My goal is to have the `VERSION` file at the root of the checkout directory, defined in only one place. I also want users to be able to inspect the version at runtime from python.