Very minor version includes mostly documentation updates in preparation
for a public alpha release.

Realised that the Vim plugins I see (and the ones I've written
previously) use the name of the help file as their main first tag,
namely using a `.txt` extension. Let's go with that convention.

List the plugin's external dependencies, currently only `mplayer` which
is used to play game audio.

List a few known bugs that currently appear in the game.

Originally thought of Maize but had misspelled it as Maze. Was
considering Maiz so as to not be so literal, then decided that a more
French spelling looked nicer.

Write Vim help for the plugin including an introduction, information
about the command and map provided, as well as gameplay instructions and
maps.

Also generate help tags.

Change the backstory based on my Dad's recommendation that the enemy
ships should be popcorn kernels. This makes the story more fun and weird
and pacifistic.

Another possible idea from my conversation with my parents is that the
kernels could pop into popcorn when you hit them, and this would turn
them into collectibles. Let's see if I have time to make that work.

Initial ideas for the backstory of the game.

Setup layout and structure of the code.

* Add a command and map to start the game
* When the game is started, prompt for game start, help, or leaderboard
* Create help file template (TODO)
* On game start, initialise the board with spaces and a player character
* Setup buffer locals on game start
* Create various functions that we'll need coming up either as stubs or
  filled in with what they'll probably be.