Add the route-guide example for v2

[glbrntt]

Motivation:

Examples help illustrate how to use gRPC. The route guide example
is also the base for one of the "standard" gRPC tutorials.

Modifications:

• Add a route-guide example for v2

Result:

More examples.

[glbrntt]

This is split across two commits:

• 3787045 adds the generated code
• 8eddb1f contains the 'real' changes