Consistency between Slot/Round/Epoch/Schedule

[lbarman]

In the paper,
A slot is a upstream cell, for one client
A round contains N slot, one for each client
An epoch is a succession of rounds between two resync's
A schedule assigns each slot of a round to a client

Unfortunately, this is not the case in the code, especially because a round is [1 downstream message]+[N upstream messages].

Proposed terminology:
A cell is on byte message (up- or downstream)
A round is N+1 cells, 1 downstream, N upstream (that gets XORed into one message)
A slot is a position in the schedule
An epoch is a succession of rounds between two resync's
We have no terminology for a succession of N rounds.