Merge pull request #6 from jkozlowski/master

Add top-level documentation.
Added cabal sandbox files + TAGS to .gitignore
Added commit index to types and to Follower code
CSetCommitIndex generation for leader
Some cleanup of 'udp' example
Forgot to update commit index in node state
Updated 'udp' example to use CSetCommitIndex
Minor cleanup: some formatting and redundant constraint removed
Merge pull request #9 from qrilka/commit-index

Implement commit-index propagation