Instrumenting Deployment Artifacts (major site doc enhancement and small plugin enhancement)

It is occasionally useful to measure the code coverage for manual and/or
automated tests which run against a test environment.(Not to be confused with
measuring code coverage of unit tests executed automatically by the
build system.) For example, you may have a set of automated regression
tests written using JMeter, Selenium, etc. which for some reason or
another are not appropriate to run as part of the maven build.

The primary difficulty in supporting the above use case is understanding
what needs done, and then to a limited extent configuring Maven appropriately.
To that end I have added a new "Instrumenting a Deployment Artifact" section
to the Maven Cobertura plugin's site documentation. I have attached a PDF
showing the html rendered version of the enhanced documentation
(source documentation file is in the usual apt format).

In addition to the documentation enhancements, I have extended the instrument goal
to support registering a module's cobertura.ser file as an attached artifact.
This turns out to significantly clean up the child modules of a multi-module
project, which would otherwise be cluttered with build-helper plugin configuration
details.

The attached patch file contains all of my changes. I look forward to a
release in the near future which contains these changes, provided they
are deemed acceptable by the project maintainers.