Update c++ examples.

Ensure that client generated methods don't conflict with other properties

Add roots.pem to Grpc C# nuget package

Prevent using the hosts cache with a nil address

Remove redundant Node route guide examples

Python Beta codegen.

Adding C++ auth metadata processor.

Grpc ruby server add support for multiple certs

Metadata and serialization for Python

- allows use of multiple credentials, e.g, per servername

The rest of the Python Beta API

Fix gRPC links lifecycle tracking

Drop invoker during test tear-down

Fix grace period bug in _end.accept_ticket

php: fix gce testing dockerfile

Grpc ruby fix math client and server

Update debian source instruction

(1) Plumb the metadata transformer given at the Beta API through to the
InvocationLink where it will be used.

(2) In both InvocationLink and ServiceLink, if there isn't a registered
serializer or deserializer, just pass the payload through rather than
ignoring the entire RPC.

- The processor now belongs to the server credentials in core.
- The server credentials now needs to be refcounted.
- Changed slighly the vtable of credentials to make it easier to avoid
  memory leaks (free'ing the pointer is now done at the common layer,
  the implementations of the creds are now only reponsible for
  destructing the implementations' specific members.

Tracing api

The invoker is an object derived from, and referring to, objects of the
Face implementation under test. If those objects are to be garbage
collected at the appropriate time the invoker that references them must
be made eligible for garbage collection in the test's tearDown method.

Tickets should not be ignored if the end is in a grace period; rather
they should be ignored if they are for an unrecognized (likely new)
operation and the end is in a grace period.

Provide troubleshooting instructions for 'cannot load grpc_csharp_ext.dll' problem

- ensures that servers cancels calls after the shutdown timeout
- uses an infinite timeout when request server calls

This two changes fix the issue where the server segfaults on shutdown.