2020.730 (beta)

This release involves significant refactors and accessibility reductions.

• Adds Request-Level Headers
• Removes PerformLast<T>() and PerformLast()`
• Moves most of the virtual methods. To achieve the same result, override the method by overlaying it (i.e in your client make an identical method to the base and use that instead)
• Add Perform<T>() for a pre-fabricated HttpRequestMessage
• Add a handler wrapper for redirecting and keeping the auth header
• Removes ~60% duplicated code