rename Maven modules

previously i'd just echoed the code name in the module name,
so i expanded them to more human-friendly names
(e.g. spec → Specification, impl → Implementation).
add parent POM to build child modules

configured a parent Maven project to build each of the three
child projects (spec, impl, inst). this makes it easier
to step back and build "everything" from the project root,
while retaining individualized settings for each sub-project.