Better semver ranges support 

As of version `1.0.0` it only supports ranges in the form `~1.2.3` as it seems to be the only kind of range used in `d3` modules.

For example, if instead of

``` js
var MODULE_NAME = 'd3'
```

we use

``` js
var MODULE_NAME = 'backbone'
```

we get an error when processing a range like `>=1.1.2` which I'm not supporting at the moment.
