Allows settings to be overwritten on a per-project base

If you create a `settings` area on your `Project.sublime-project` file and you override settings of the original `RubyTest.sublime-settings` file, it will read the properties from that file that instead.

Example:

```javascript
{
	"folders":
	[
		{
			"follow_symlinks": true,
			"path": "crm_bliss"
		}
	],
  "settings":
  {
    "run_rspec_command": "arspec {relative_path}",
    "run_single_rspec_command": "arspec {relative_path}:{line_number}",
  }
}
```