add capability to bootstrap from DNS
Add a simple test and mock for genDNS
fix from comments
add apurl checking and logging
Documentation: update to 2.0

In anticipation for a 2.0.0-rc.0 release update and move the
documentation.
version: bump to v2.0.0-rc.1
logos: add SVG and PNG logos
Merge pull request #1963 from robszumski/add-logo

logos: add SVG and PNG logos
raft: leader waits for the reply of previous message when follower is not in good path.

It is reasonable for the leader to wait for the reply before sending out the next
msgApp or msgSnap for the follower in bad path. Or the leader will send out useless
messages if the previous message is rejected or the previous message is a snapshot.
Especially for the snapshot case, the leader will be 100% to send out duplicate message
including the snapshot, which is a huge waste.

This commit implement a timeout based wait mechanism. The timeout for normal msgApp is a
heartbeatTimeout and the timeout for snapshot is electionTimeout(snapshot is larger). We
can implement a piggyback mechanism(application notifies the msg lost) in the future
if necessary.
readme: add logo
Merge pull request #1962 from xiang90/raft

raft: leader waits for the reply of previous message
Fully resolve DNS entries to IPs and ignore single errors (such as no etcd-server-ssl)
Merge pull request #1964 from robszumski/master

readme: add logo
rename flag to discovery-srv
Fix building the lock on windows
move constants out for windows
Add notification in docs re backup command
apologize profusely about locking on windows
Merge pull request #1961 from barakmich/flock

Fix building the lock on windows
*: change remaining 0.5 references -> 2.0