Add munit for unit testing.

Main method extracted to separate file to make it easier to test the _rest_ of the code.
munit is added as a submodule by running `cd src; git submodule add https://github.com/nemequ/munit.git` .

Unit testing has so far only been tested on ubuntu.

.gitignore

@@ -71,3 +71,12 @@ lib/plrobjs/index
 /lib/etc/last
 # or mail
 lib/etc/plrmail
+
+# test object files, etc
+src/test/depend
+src/test/*.o
+src/test/testfile
+
+
+# ide etc.
+.vscode