Fixed Ruby build on Mac

Update Ruby README with simpler install instructions

Update C# examples to 0.12.0 packages.

Re-ordering interdependent proto files.

Revert "Refreshing the etc/roots.pem file."

This reverts commit 64279c7c.

The new roots.pem is not compatible with default boringssl.

Fix a bug recently reported in the mailing list

Use specific ruby thread to handle auth metadata plugin callbacks

Use core metadata validation functions in Node library

Make metadata validation functions reject empty keys

Make the Ruby extension throw an error when passed invalid metadata

Update some Node dependencies to more recent versions

Expose core metadata validation functions in public headers

Update Ruby library version for next release

Backport copyright changes

Security connector fixes for 0.12 branch