Implement initial game loop

[matthewjwhite]

Implements https://github.com/matthewjwhite/crystal-skull/issues/5.

Basic flow:

• User authenticates.
• Determines whether to enter battle.
  • If it's time, User::battle is called with a random monster from the configuration file.
  • The battle continues using randomized hits based on the user and opponents' strength.
• If it's not time to battle, the user is given the option to navigate in a particular direction.
• Finally, they are given the option to continue. If they reply with N/n, then the connection dies.

[matthewjwhite]

Two major concerns:

• As the user is fully fleshed out, it will become cumbersome having a new parameter to User::init for each user statistic/attribute (#7 will dig into this).
• Duplicate statistic information shared between monsters and users is something that should be combined at some point, or handled in a better way than using duplicate code.