docs: clean up other apis

The docs for the other APIs use curl for example usage, which matches
the docs for the etcd APIs.

Other cleanup include fixing usage of peer ports and using 10.0.0.x IPs
throughout.
etcdserver: improve panic message in Cluster
cluster: separate out membersFromStore from newClusterFromStore
Merge pull request #1618 from yichengq/203

etcdserver: improve panic message in Cluster
etcdserver: move config validation to cluster
Merge pull request #1623 from xiangli-cmu/valid_configuration

Valid configuration
discovery: simplify interface

There's no real need to expose a Discoverer interface/struct when the
only use of the interface (and indeed the module) is to invoke a single
function. This isn't Java, after all. So instead, simplify to Discovery
exposing just two functions: JoinCluster (i.e. what was formerly called
"discovery"), and GetCluster (hitherto "ProxyDiscovery")
etcdserver: validate peerurl when adding members
Merge pull request #1625 from yichengq/205

docs: describe the lifetime of discovery url
Fix typo in docs

Suggesting that users add two nodes with the same name is probably not a
good idea.
Merge pull request #1629 from asmundg/x-fix-typo

Fix typo in docs
Merge pull request #1626 from jonboulle/proxy_stuff

discovery: simplify interface
Merge pull request #1627 from xiangli-cmu/validate_peer_url

etcdserver: validate peerurl when adding members
Merge pull request #1585 from coreos/clean-up-other-apis-docs

docs: clean up other apis
etcdhttp: return 409 instead of 412 when there is a conflict when adding a member
etcdmain: use StringsFlag for initialclusterstate
doc: document conflict case when adding a member
Merge pull request #1631 from xiangli-cmu/validate_doc

Validate doc
client: add error handling for addmember
Merge pull request #1632 from jonboulle/cs_flag

etcdmain: use StringsFlag for initialclusterstate