Add support for binary data

[bojand]

Add support for binary data input. Addresses #22.
Added two new options:

-b  The call data comes as serialized binary message read from stdin.
-B  Path for the call data as serialized binary message.

Example usage:

ghz -proto ./greeter.proto -call helloworld.Greeter.SayHello -B ./hello_request_data.bin 0.0.0.0:50051

Or using binary from stdin:

ghz -proto ./greeter.proto -call helloworld.Greeter.SayHello -b 0.0.0.0:50051 < ./hello_request_data.bin