[CHEF-5021] Include "files" var which adds to install_path

This includes the ability to include files/folders outside of
/opt/{project} that you may want included in the full package.
Add files method to set or read the files string or array

This commit adds a files method so that you can either set or read
the files string or array.  This allows initial for testing to
inspect the value of @files.
Remove unnecessary blank lines
Call it extra_package_files to be more verbose

Add note that this only works for RPM, DEB and Makeselfinst
Merge pull request #92 from petecheslock/master

[CHEF-5021] Include "extra_package_files" var which adds to install_path