License everything under the GPL version 2

Makefile

@@ -1,4 +1,18 @@
-### If you fail to build, run 'make deps'! ###
+# The GPLv2 License (GPLv2)
+# Copyright (c) 2023 Jeremy Baxter
+# 
+# esv is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+# 
+# esv is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU General Public License
+# along with esv.  If not, see <http://www.gnu.org/licenses/>.
 
 PROG      = esv
 IMPORT    = import