Use static factory methods and proxyBeanMethods = false

It is better to be explicit about beans of type `Module` and make
sure they don't interfere with Spring trying to enhance
`@Configuration` classes. The tests are now clear of the pesky
warning logs, and there is a new section in the README.

src/test/java/org/springframework/guice/module/DevelepmentStageInjectorTest.java

@@ -65,7 +65,7 @@ public class DevelepmentStageInjectorTest {
 	static class ModulesConfig {
 
 		@Bean
-		TestGuiceModule testGuiceModule() {
+		static TestGuiceModule testGuiceModule() {
 			return new TestGuiceModule();
 		}
 

src/test/java/org/springframework/guice/module/SpringModuleWrappedTests.java

@@ -79,7 +79,7 @@ public class SpringModuleWrappedTests {
 	protected static class ModuleProviderConfig {
 
 		@Bean
-		public ProviderModule module() {
+		public static ProviderModule module() {
 			return new ProviderModule();
 		}