Add test for --source flag and pull request suggestions

Add a demo/sourcing.vars file to be used by the associated demo
script.

Modified mo argument parsing so that --help and --source=file do not need
to be the first arguments for mo. And can in fact appear after or in the
middle of filenames.

demo/sourcing

@@ -4,11 +4,6 @@
 
 cd "$(dirname "$0")" # Go to the script's directory
 
-cat <<EOF >sourcing.vars
-export NAME="Alex"
-export ARRAY=( AAA BBB CCC )
-EOF
-
 cat <<EOF | ../mo --source=sourcing.vars
 Hello, my name is {{NAME}}.
 And this is ARRAY's conntents:

demo/sourcing.vars

@@ -0,0 +1,2 @@
+export NAME="Alex"
+export ARRAY=( AAA BBB CCC )