This version release is on account of the following "it actually does
things" improvements:

* Infrastructure:
    * Implemented `Universe` type which holds all should-be-persistent
      game state and arbitrary graph references. (Still undecided on
      whether this should turn into entity-component-system.)
    * Increased speed of raycasting.
* Web client:
    * Added texturing for detail on recursive blocks.
    * You can click on blocks to remove them (but not to add them).
    * The keyboard focus defaults to where it will actually do things,
      rather than you having to click on the canvas.