Add Maven build as convenience for installing/deploying to a Maven repos...

For discussion:

Many people/projects use Maven or another dependency management tool such as Ivy.  This PR adds a Maven POM file to the project so that a Maven artifact can be built.

I have *not* added this to the makefile, and Maven is not configured to build/re-use anything that ant has done; it is entirely in parallel.

Perhaps the correct solution here is to call Maven from ant in the latter's build.xml, but at least this PR provides a POM file for discussion, and the Maven parts can be completely ignored by people who don't use Maven (provided the documentation is updated to explain the pom.xml's presence)