* augments grpcurl package API in order to handle multiple formats
* deprecates old signature for InvokeRpc
* add command-line flag to use protobuf text format instead of JSON
* use AnyResolver when marshaling to/from JSON
* support go modules
- use Go 1.11 (with and without module support) in CI
- add go.mod and go.sum files
- with modules in Go 1.11, can't rely on GOPATH directory layout, so just copy test.proto into this repo
Joshua Humphries