Fixes #7 - Add support for using a url as the source

### What is the problem / feature ?

It'd be nice to be able to use the URL of a schema as a source for `flex.core.load`

### How did it get fixed / implemented ?

Added support for using a url to `flex.core.load_source`

### How can someone test / see it ?

Use a url as the source of a schema.

*Here is a cute animal picture for your troubles...*

![sun_bear1](https://cloud.githubusercontent.com/assets/824194/4971149/d9da5e08-6891-11e4-92bb-7c8d00282cd1.jpg)