GH-461 Add to register more than one functional class

Similar to the way we allow multiple functions to be listed with 'definition' property, this enhancement allows several functional classes to be deployed

Resolves #461

spring-cloud-function-deployer/src/it/bootjar/src/main/java/function/example/ReverseFunction.java

@@ -0,0 +1,13 @@
+package function.example;
+
+import java.util.function.Function;
+
+public class ReverseFunction implements Function<String, String> {
+
+	@Override
+	public String apply(String value) {
+		System.out.println("Reversing " + value);
+		return new StringBuilder(value).reverse().toString();
+	}
+
+}