Basic, debugged, Paxos implementation

This does not implement MultiPaxos, preferring to do each round
individually.  It's super-inefficient!
rename message to all-caps, better words
split cluster up into a sequence of developing files
Merge pull request #4 from djmitche/introduce-cluster

Introduce cluster
* Beginning of a spreadsheet/ directory.

  Eventually it'll become a miniature version of SocialCalc,
  intended to illustrate GHC->JS compilation.