Now the generated code doesn't need to check for end group tags, as it will skip whole groups at a time.
Currently it will ignore extraneous end group tags, which may or may not be a good thing.
Renamed ConsumeLastField to SkipLastField as it felt more natural.
Removed WireFormat.IsEndGroupTag as it's no longer useful.

This mostly fixes issue 688.

(Generated code changes coming in next commit.)

Change ReadTag/PeekTag behaviour to return 0 at EOF

We don't need to expose the InvalidProtocolBufferException factory method now that the generated code doesn't throw the exception.

Change ReadTag and PeekTag to just use 0 as a return value for "end of stream", rather than using an awkward out parameter.
This simplifies quite a lot of code.

Generated code in next commit.

C# conformance tests

We should now have no conformance failures.

This is expected to be the cause of the conformance test failures.
Generated code in next commit.

The tests are run from Travis in the same way as on other
platforms. Currently some expected failures - but only expected
in that they're what we got to start with. Will try to fix them in
other pull requests.

Completely untested so far - easier to get started in VS and then transfer to Linux for tweaking...

Document everything, and turn on errors if we fail to document anything in the future

Fix build warnings around unused variables

Various compilation fixes

JSON formatting for FieldMask

Remove a redundant layer of directory hierarchy.

Allow partially-trusted callers again.

Expose Coded*Stream constructors directly.

Fixes issue #552. (And yay, it looks like our build profile supports this...)

Add ReleaseSigned configuration for C#

Formatting of Struct as JSON

This seems remarkably little code, but it appears to work. I can add tests for invalid structs at some point, once the general approach is approved.

JSON formatting for Timestamp and Duration

This is taking an approach of putting all the logic in JsonFormatter. That's helpful in terms of concealing the details of whether or not to wrap the value in quotes, but it does lack flexibility. I don't *think* we want to allow user-defined formatting of messages, so that much shouldn't be a problem.

Simpify json tests

Fix C# JSON field ordering

Fix build failure on Windows when Unicode build is enabled.

Fix trivial bug in field orderings.