[build] build is now far less unreliable

Tiered compilation used to dump every stage into the same build dir, and included that dir on the classpath,
which means any ordering issues introduced into a build aren't going to result in a failed build,
thus breaking the build for everybody except those who already had a working lombok in their
build dir before starting a build. The opposite of bootstrapping, in other words.

Fixed by having each stage build into its own private stage phase.

buildScripts/website.ant.xml

@@ -217,7 +217,7 @@ such as applying the templates to produce the website, converting the changelog
 			<package name="lombok" />
 			<package name="lombok.experimental" />
 			<package name="lombok.extern.*" />
-			<classpath location="build/lombok" />
+			<classpath location="build/lombok-main" />
 			<header><![CDATA[<a href='https://projectlombok.org/' target='_blank'>Lombok</a> - ]]>v${lombok.version}</header>
 			<bottom><![CDATA[<i>Copyright &copy; 2009-${javadoc.year} The Project Lombok Authors, licensed under the <a href='http://www.opensource.org/licenses/mit-license.php' target='_blank'>MIT licence</a>.]]></bottom>
 		</javadoc>