Battleship board game implementation in Turtle

[sathwikmatsa]

This PR adds battleship board game implementation to turtle examples - #23

• [x] single player mode
• [x] multiplayer mode
• [x] arrow keys & enter based controls

[enaut]

Firstly - I don't have commit rights here!

I did not really read the whole code. But at a first glance, I think it would be nice to have some more documentation - as the examples are made to be read for learning. The audience is less experienced and is often very happy for explaining comments - so an overview in main.rs over the code might be helpful, as well as some function documentations for the less obvious things...

That said, the game itself looks great!

[sathwikmatsa]

Hey @enaut, Thanks for your feedback. I've added some documentation as per your suggestion. Let me know if you have any comments.

[sunjay]

Thanks for taking the time to contribute this example! Appreciate the first pass at reviewing @enaut. I have been swamped with things at work lately but hopefully I will have time to review this in the coming week. If I don't get to it by next weekend, please ping me. Sorry for the delay!