Change Go starter package

I'd like to change the Go starter for the following reasons:

1. Idiomatic Go: this package adheres to the standards and style of the Go language.
2. Tests: these help reinforce the integrity of the game logic and client.
3. Game logic: includes more of the structure and ideas found in the [Python starter](https://github.com/ornicar/vindinium-starter-python).
4. Client complete: provides all options available when running in either arena or game mode.

https://github.com/geetarista/vindinium-starter-go