Changes behavior of input and output directories.

For output directory: if we cannot create output directory,
we throw an exception and log it (warning level). For input
directory: removes default value and gets this value from
maven project or directory specified by the user.
Adds a logging to build reports.

Adds logging system to build a result xml file for
each module of a maven project. For a simple project,
the result file will be generate to target/spoon-maven-plugin
folder of the project. For multi module project, the
result file will be generate in each target/spoon-maven-plugin
folders of each module.
Merge pull request #3 from GerardPaligot/fix_output