Memory registry from #801 with additional tweaks (#951)

* PoC: memory registry using maps instead of slice madness

* Updated proto and handlers. Fixed tests across codebase.

* Implemented ttl pruning for memory registry

* Added extensive memory registry tests

* Squased a bunch of bugs

* Proto indent; memory.Registry.String() returns "memory"

* Write a test to prove memory registry TTLs are busted

Signed-off-by: Erik Hollensbe <github@hollensbe.org>

* Additional memory testing and fixups:

* DefaultTTL removed
* When TTL == 0, it is automatically removed from expiry conditions
* Additional improvements to new tests

Signed-off-by: Erik Hollensbe <github@hollensbe.org>

service_test.go

@@ -29,8 +29,7 @@ func testService(ctx context.Context, wg *sync.WaitGroup, name string) Service {
 	// add self
 	wg.Add(1)
 
-	r := memory.NewRegistry()
-	r.(*memory.Registry).Services = testData
+	r := memory.NewRegistry(memory.Services(testData))
 
 	// create service
 	return NewService(