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

scripts/release-version

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