sqapi: add methods new_month and new_year

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7004 8aca7d54-2c30-db11-9de9-000461428c89
sqapi: document get_map_file

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7005 8aca7d54-2c30-db11-9de9-000461428c89