Improved filesystem efficiency

Previously, `sheets.print()` would query the filesystem every time it
was invoked. This was inelegant, because it is called multiple times
every time `cheat` is executed. Thus, unnecessary calls were being made
out to the filesystem.

Now the result of that function is being buffered into a module variable
when it is executed the first time, and served from there thereafter. I
broke the "functional" paradigm to a degree by doing this, but it wasn't
worth the complexity of implementing proper memoization (decorators,
etc) for such a trivial case.

Bumped the version number accordingly.