Added POM rules to generate javadoc and sources JARs for Expect4j

Expect4J now produces 3 JARs: (1) the library itself, (2) a copy of the
source code for the library, and (3) the generated javadocs for the
library.  These last two can be used in conjunction with varous
editors/IDEs (such as Eclipse, amongst many) which can help provide
context to the coder.