The example utilizes native bazel rules (proto_library, cc_proto_library,
java_proto_library, java_lite_proto_library) to show how easy it is to
build protobuf with bazel's native support. It also makes use of well
known types which was not possible until the latest bazel 0.5.4 release
and https://github.com/google/protobuf/pull/3594 .

Since these tags might be confusing, added a note that these are not
part of the normal protocol buffers syntax.  I also linked to the main
tutorials page that uses these examples
https://developers.google.com/protocol-buffers/docs/tutorials so that
anyone who arrived here without going through that info first can get
more explanation if they want.

Note that now we need a proto3 version of addressbook.proto. This may affect other platforms, and could do with an overhaul to follow proto3 conventions anyway (e.g. repeated field names). Will need to think about that carefully before merging into master. Raised issue #565 for this.

- Remove some old proto2-based C#-only messages
- Remove the "build" directory which only contained out-of-date files
- Remove the csharp_namespace option from proto2 messages
- Change "Google.ProtocolBuffers" to "Google.Protobuf" in other messages

To my surprise, executing generate_protos.sh used the version of Bash installed with Git for Windows by default.
After a few modifications to detect the most appropriate protoc to use, this worked pretty simply.
This change also:
- adds generation of the address book tutorial proto,
- fixes the addressbook.proto to specify proto2 explicitly (to avoid a warning from protoc; I don't think we want warnings...)
- fixes the addressbook.proto C# namespace (which I thought I'd done before, but apparently hadn't)
- includes the regenerated UnittestCustomOptions.cs apart from the DescriptorProtoFIle => Descriptor change

committer: Jon Skeet <skeet@pobox.com>