Supports processors when the plugin spoon a project.
Improves pom.xml of the project.

Rollback to 2.3.1 spoon's version, changes groupId
and version of the plugin in the pom.
No more spoon project already spoon
Makes possible to launch spoon with processors in command line.
refactors package of the plugin.
Updates README and cleans gitignore file.
Prepares pom.xml for the release to maven central

Adds gpg plugin in a profile to signs jar files only
when we make a release and changes the groupId to
correspond to the groupId of spoon project. Changes
the version of spoon to the latest, 2.4.

Rollback to spoon version 2.4.
Fixes bug when the developer would like specify his input folder.