build.yaml changes to make certain grpc++ builds work

remove futures from py3

allow choosing config of ruby package builds from environment variable

Lower-case example "Authorization" header name in doc string

Python grpc.secure_channel doc string correction

PHP: reject metadata keys that are not legal

The HTTP/2 specification requires header names to be lower case.

PHP: remove extra comma

Let tracing be enabled before starting an RPC

Rename some files to avoid conflicting .obj files on Windows

by calling grpc_init on [GRPCCall load], instead of lazily.

PHP: bump version

update dependencies in C# examples to GA versions

update to system interactive in distrib tests

Truncate Python example READMEs to grpc.io links

Remove unused imports in grpcio-tests

PHP: remove reference to beta in INSTALL.md

Dont catch load error when loading grpc lib in ruby gem