Simplify Request body, add parseFormUrlEncoded

[lukewilliamboswell]

This PR;

• Simplifies the Request body and mime type by removing the InternalBodyBody workaround which was a workaround to get the initial basic-webserver implementation working with glue.
• Adds the Http. parseFormUrlEncoded helper for parsing URLs and Form data
• Regenerated glue (and cargo fmt'd)

[Anton-4]

I'm almost done reviewing, will finish up tomorrow :)

[Anton-4]

Thanks @lukewilliamboswell!