Add options to Node library to modify ProtoBuf behavior

Increase Node's per-test timeout and Ruby's overall test timeout

Fixed refactoring of grpc_arg pointer vtable

Subchannel Sharing  [The interop tests failures and Basic test failures are unrelated to this change. Merging]

Provide explicit API for user to set user agent string prefix

Add an open-loop test using Poisson at 20-70% of peak

Flagging the missing API entries.

Add a NullLogger in the C# implementation

Extern "C" Python DLL support

I'd argue that at this stage, this should probably be the default. Further options to consider:

- Make it a singleton, or at least expose a static property with a single instance?
- Allow SetLogger(null) to use the NullLogger?

Fix pygrpc_load_core in pxi to match with the C definition

Fix copyright

Add a sanitize script usable in a precommit hook

Fix the arguments type for on_read and destroy callbacks in iomgr

Fix PHP copyright