feat(version): generate version from git tags

This will generate the version based on git tags. So if it is built
directly on a tag it will use the tag name and if it is built off a
commit that isn't a tag it will look like:

    $ curl localhost:7001
    0-267-ga39cf1c

.gitignore

@@ -1,2 +1,3 @@
 src
 etcd
+release_version.go

build

@@ -21,4 +21,5 @@ for i in third_party/*; do
 	cp -R $i src/
 done
 
+./scripts/release-version > release_version.go
 go build ${ETCD_PACKAGE}

scripts/release-version

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+VER=$(git describe --tags HEAD)
+
+cat <<EOF
+package main
+var releaseVersion = "$VER"
+EOF

version.go

@@ -1,5 +1,3 @@
 package main
 
 var version = "v1"
-
-var releaseVersion = "etcd pre-0.1"