Get 2.0 (Beta 1)

This release is a quick follow-up to Get 1.0 that fixes some of the shortcomings of the original design of the Request type.

• Request can now be initialized with either a string (path: String) or a URL (url: URL)
• Replace separate .get(...), .post(...), and other factory methods with a single HTTPMethod type. Example: Request(path: "/user", method: .patch)
• The first parameter in the Request initializer is now path or url, not method that has a default value
• Add a new Request initializer that defaults to the Void response type unless you specify it explicitly
• Make body property of Request writable
• Add upload(for:data:) method - #50, thanks to @soemarko
• Replace APIDelegate client(_:makeURLFor:query:) method with client(_:makeURLForRequest:) so that you have complete access to the Request
• Remove APIs deprecated in Get 1.0

See #51 for the reasoning behind the Request changes