Initial creation of OwinRailway.
Parameterize exception handling in the OwinRailway.
Add With member for immutable updates.
Update Railway implementation, including failing test cases.
Fix error in With member.
Fix failing railway test.
Replace Contracts calls with simple asserts.
Async copy streams
Rename f to handler
Update invokeHttpResponseMessage signature
Adapt System.Net.Http-based handlers to use the OwinRailway.
Complete railway implementation.