Leader should choose when to use RS-coded data

[btmorr]

Given F, the number of nodes that can fail and the cluster remains alive, and k (per #93), when appending new logs the leader should guess who many nodes are currently responsive (based on data stored per #92), and if the number of responsive nodes is greater than or equal to F+k, the leader should use (k,m) RS codes to federate the data among the cluster (https://github.com/klauspost/reedsolomon).