#76 allow plugin for customized output printer

[Feng Qian]

I use EMMA for measuring Java code coverage. We also
need to store row historical results (filename,
linenumber, and hits) in the database. Currently we are
using a common format for results of other languages.
It would be nice to allow a customized report printer
to be plugged into the framework.

I have done it locally by adding one extra option "-r
other", and supplying "-Dreport.printer=<my printer>"
property. <my printer> extends AbstractReportGenerator,
and the later uses reflection to create an instance of
<my printer> when its 'create' method is called.

The change in EMMA is simple. Several lines in the
AbstractReportGenerator.create method. If people think
this is useful, I can make a diff file and contribute
back to the project.

[Feng Qian]

my changes on AbstractReportGenerator.java