[setup.cfg] always use --pyargs option with pytest to re-enable doctests discovery

The --pyargs option makes pytest try interpreting arguments as importable python package names, or if that fails treat them as normal filesystem paths.

Now running `pytest` command will automatically run all the tests in "Tests" folder, as well as the embedded doctests in the installed "fontTools" package.

This is in reply to a comment by Behdad in
fdbf066a8c

setup.cfg

@@ -40,6 +40,7 @@ license_file = LICENSE
 minversion = 3.0
 testpaths = 
 	Tests
+	fontTools
 python_files = 
 	*_test.py
 python_classes = 
@@ -49,4 +50,4 @@ addopts =
 	-r a
 	--doctest-modules
 	--doctest-ignore-import-errors
-
+	--pyargs