Pre-compute the Bukkit/Spigot download URLs

For #77

minecraft-server/get-mcadmin-versions.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+if [ $# -lt 1 ]; then
+  echo Missing arg: URL
+  exit 1
+fi
+
+cd /tmp
+wget -O mcadmin-versions.jar https://bintray.com/itzgeoff/artifacts/download_file?file_path=me%2Fitzg%2Fmcadmin-versions%2F1.1.0%2Fmcadmin-versions-1.1.0.jar
+wget http://central.maven.org/maven2/org/jsoup/jsoup/1.9.1/jsoup-1.9.1.jar
+
+java -jar mcadmin-versions.jar $1 > /tmp/mcadmin-versions.db
+rm *.jar