Changed the sharecraft command from / to ! and added it to the !help command output.

Hi there!  I noticed that the !help command in chat didn't say anything about how to share a craft file, and then with a little more research was perplexed to find that the /sharecraft command seems to be the only chat command preceded by a slash instead of an exclamation point.

I changed that, and added details about sharecraft to the output of the !help command.

Hope you'll like the idea!  Please feel free to tell me if there's something I'm don't know here that makes this all not make sense.