raft: set none to be 0
etcdserver: fix testServer
raft: use const firstId to track ids
wal: add a doc file
wal: add more explanation to wal filename format
wal: wal.OpenFromIndex -> wal.OpenAtIndex

The first entry read from the wal should be the index provided. This
name makes that more clear.
raft: test node step
Merge pull request #1054 from philips/add-wal-doc

wal: add a doc file
raft: comments for TestNodeStep
raft: set From of local message to be local id
raft: use [1,n] as address list for raft state machines
raft: use raft helper function in testing
raft: remove vote with default value
Merge pull request #1060 from jonboulle/peers

etcdserver/etcdhttp: split out peers and add tests
raft: add a doc.go file

Explain the package from a high level.
raft: add useful comments

These comments were things I learned about the units, use case or
meaning of various fields and functions in the raft package.
Merge pull request #1059 from coreos/node_test

test node step
wal: change wal filename format

Make raftIndex section to be expected raftIndex of next entry.

It makes filename more intuitive and straight-forward.

The commit also adds comments for filename format.
Merge pull request #1045 from unihorn/119

wal: change wal filename format
raftLog: compact applied entries only

compact MUST happen on entries that have been applied, or
1. it may screw up the log by setting wrong commitIndex
2. discard unapplied entries