First pass at the big rename from ProtocolBuffers to Google.Protobuf.

We'll see what I've missed when CI fails...

C# wrapper types

Export c# naming routines publicly

Fix make distcheck

Run C# tests on Appveyor

- We do still generate the message types, as otherwise reflection breaks, even though it doesn't actually use those types.
- JSON handling hasn't been implemented yet

Remove the struct-based iterator for RepeatedField.

We don't use it in the runtime or generated code anywhere now, so the extra small performance boost isn't as critical, and it has some undesirable consequences.

The tests have needed to change as iterator block enumerators don't throw when we might expect them to.

Assorted nits from C# code.

Update csharp-experimental with changes from upstream/master

Don't generate types for map entry messages

I'm sure I've implemented this before, but somehow it's been lost in a maze of twisty little branches, all alike.

Introduce C# well-known types

This involves:
- Specifying a namespace in each proto (including ones we'd previously missed)
- Updating the generation script
- Changing codegen to implement IReflectedMessage.Fields explicitly (a good thing anyway)
- Changing reflection tests to take account of the explicit interface implementation

Non-generated code in this commit; generated code to follow

Change the reflection namespace in C#

Update code already within Google.Protobuf.Reflection which was importing Google.Protobuf.DescriptorProtos

Change the C# namespace in descriptor.proto to Google.Protobuf.Reflection.
This then means changing where the generated code lives, which means updating the project file...

It also involves regenerating the C++ - which has updated the well-known types as well,
for no terribly obvious reason...

Generated code changes from previous commit

- Move types into Google.Protobuf.Reflection
- Change codegen to reflect that in generated types

Generated code changes coming in part 2

Pascal-case namespace automatically in C# codegen

Fixes issue 312.

JSON formatting in C#

- Remove the indexers in FieldAccessorTable
- Add a TODO for field ordering in oneof

remove pbconfig from extract script

Change-Id: I5049da7449cbada781aa1e23485a336b584802cb

Added support for JSON and valid input to conformance tests.