update and fix checkstyle and javadoc plugins

.vscode/settings.json

COPYING

README.md

pom.xml

src/main/config/checkstyle.xml

...n/java/net/sourceforge/plantuml/servlet/AsciiServlet.java

.../java/net/sourceforge/plantuml/servlet/Base64Servlet.java

.../net/sourceforge/plantuml/servlet/CheckSyntaxServlet.java

...ava/net/sourceforge/plantuml/servlet/DiagramResponse.java

...ain/java/net/sourceforge/plantuml/servlet/EpsServlet.java

...java/net/sourceforge/plantuml/servlet/EpsTextServlet.java

...ain/java/net/sourceforge/plantuml/servlet/ImgServlet.java

...ava/net/sourceforge/plantuml/servlet/LanguageServlet.java

...ain/java/net/sourceforge/plantuml/servlet/MapServlet.java

...ava/net/sourceforge/plantuml/servlet/OldProxyServlet.java

...ava/net/sourceforge/plantuml/servlet/PlantUmlServlet.java

...n/java/net/sourceforge/plantuml/servlet/ProxyServlet.java

...ain/java/net/sourceforge/plantuml/servlet/SvgServlet.java

...a/net/sourceforge/plantuml/servlet/UmlDiagramService.java

src/main/java/net/sourceforge/plantuml/servlet/Welcome.java