Add tap gesture to provide additional feature info

[mfcollins3]

I enhanced RoadmapFeature by adding a url property that can be used to display additional information about the feature request, such as a GitHub issue or a blog post.

I enhanced RoadmapView by adding a bindable variable for the selected feature in the list. I added a tap gesture recognizer that will update the bindable value with the selected feature. This will allow a developer to navigate to another view to show more detailed information about the feature, or to use the new url field to open a web view to show the detailed information about the feature.

I had to extend RoadmapFeature to implement Equatable. If a developer uses the new bindable field on RoadmapView and uses the onChange(of:) view modifier to react to a feature being selected, the type is required to conform to Equatable.