relax types for Bind and Render funcs

[willnorris]

This relaxes the Bind and Render to accept any type as a payload. If those types implement the Binder or Renderer interfaces, then the relevant method on the type is called. Sometimes the default Bind or Render behavior is sufficient, and I don't need any additional custom handling.

It looks like the Bind method was updated in #38 but that PR was immediately closed, but I'm not sure why.