Bounds checking for ops in call batch

Added Sandcastle project to generate C# docs

adding node, ruby, and php to cloud to prod interop tests.

Shutdown lb_policy when changing it

Added invocation of ./config

move auth property iterator declaration into auth_context.h

expose C core version string to C#

Upporting from 0.10 branch.

Improving unprotect doc.

C# Context API

Compression API, sending response headers and cleanup.

Fix gce detection

Fixes problem reading certificates file: They do come with non-ASCII chars (in comments)!

This would have caught the encoding problem with the default root
certificates.

Fix race condition in GRPCCall

Also clarify in GRXWriter.h that the writeable is released whenever the
writer finishes.