Adding the full GPL license it was apparent that the FSF recommends to
have the statements as file headers

This reverts commit 3481cc18.

external file)

branch to reflect recent changes.
The updated master branch is described in the GMD paper by Pisso et al.
(2019)

cleaned the distribution and included reference runs and comparisons

flexpart 10.4 prerelease, added read and compare output .txt files and
modified the manuscript