Add maven-central and javadoc shields

Author: ato

README.md

@@ -1,5 +1,7 @@
 JavaSWF (IIPC fork)
 ====================
+![Maven Central Version](https://img.shields.io/maven-central/v/org.netpreserve/javaswf)
+[![javadoc](https://javadoc.io/badge2/org.netpreserve/javaswf/javadoc.svg)](https://javadoc.io/doc/org.netpreserve/javaswf)
 
 This is a mavenised fork of the old
 [JavaSWF2 codebase](https://web.archive.org/web/20150711084455/http://www.anotherbigidea.com/javaswf/), to aid resolving