TLS CA Cert support
fix(etcd): remove Node.PrevValue

PrevValue is no longer in the v2 API. Remove it.
Merge pull request #68 from philips/remove-prevvalue

fix(etcd): remove Node.PrevValue
fix add valid http status codes according the change in etcd
Merge pull request #69 from xiangli-cmu/add_valid_status_code

fix add valid http status codes according the change in etcd
fix(response.go) add new http status code to error type
Merge pull request #70 from xiangli-cmu/add_valid_status_code

fix(response.go) add new http status code to error type
Merge pull request #60 from alexzorin/tls_support

Add ability to use CA Certificate to verify etcd server
feat(client.go) Add a https client; refactor related stuff
feat(node.go) add prevNode field
Merge pull request #74 from xiangli-cmu/prevNode

feat(node.go) add prevNode field
Merge pull request #73 from xiangli-cmu/httsClient

feat(client.go) Add a https client; refactor related stuff
Make tests compile again.
Merge pull request #75 from alberts/master

Make tests compile again.
refactor(delete.go) rename deleteRaw to rawDelete; be consistent with other operations
Merge pull request #76 from xiangli-cmu/rawDelete

refactor(delete.go) rename deleteRaw to rawDelete