Enhance version to allow for compact style

This is backwards compatible (i.e. doesn't change the default behavior),
but allows devs to override to get this compact style.  The style chosen
is very simple - `foobar version 1.2.3`.  Doing stuff like the GNU
standard requires some metadata about licensing which I don't want to
get into.

That being said, one could customize the format via

```ruby
version MyAPP::VERSION, :compact => true
                        :format => "%s %s\nCopyright (c) 2013 Whoever\nLicensed under Apache license"
```

To achieve this on a per-app basis.