Instrustment handlers for logging/error handling

This refactors a bit of the http handler code.
Moves error handling for handler functions to a generic handler.
This also has a side-effect of being able to propagate errors from the
provider to send the correct status code, provided the error type
matches a pre-defined interface.

vendor/github.com/cpuguy83/strongerrors/doc.go

@@ -0,0 +1,12 @@
+// Package strongerrors defines a set of error interfaces that packages should use for communicating classes of errors.
+// Errors that cross the package boundary should implement one (and only one) of these interfaces.
+//
+// Packages should not reference these interfaces directly, only implement them.
+// To check if a particular error implements one of these interfaces, there are helper
+// functions provided (e.g. `Is<SomeError>`) which can be used rather than asserting the interfaces directly.
+// If you must assert on these interfaces, be sure to check the causal chain (`err.Cause()`).
+//
+// A set of helper functions are provided to take any error and turn it into a specific error class.
+// This frees you from defining the same error classes all over your code. However, you can still
+// implement the error classes ony our own if you desire.
+package strongerrors