fix some minor errors.
There is a problem with classpath such that javadoc wasn't able to find `commons.cli` package; There are also small problems with using angle brackets `<` & `>` that caused javadoc to complain 'malformed HTML tag'. After this fix, the remaining errors are all about `@date` and `@id` tags. These are not supported by javadoc. However they don't pose a problem to the generated HTML document. So these problems are ignored for now.