prefer NoError/Error over Nil/NotNil

[trashhalo]

replaces calls to require/assert Nil/NotNil to NoError/Error

NoError is for asserting no error was return
Error is for asserting an error was returned

Why is it important?

return Fail(t, fmt.Sprintf("Received unexpected error:\n%+v", err), msgAndArgs...)

return Fail(t, "An error is expected but got nil.", msgAndArgs...)

When these fail their message explicitly calls out that we were or were not expecting an error. This communicates the intent of the assertion.