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.

tests/source.expected

@@ -0,0 +1,5 @@
+value
+* 1
+* 2
+* 3
+AAA BBB

tests/source.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+cd "${0%/*}"
+cat <<EOF | ../mo --source=source.vars
+{{VAR}}
+{{#ARR}}
+* {{.}}
+{{/ARR}}
+{{ASSOC_ARR.a}} {{ASSOC_ARR.b}}
+EOF
+
+
+# Prints the string should mo NOT fail. Meaning that the output will not match
+# tests/source.expected and therefore the test will fail.
+
+../mo --source=a/non/existent/file files >/dev/null 2>&1
+[[ "$?" -ne 1 ]] && echo "mo accepted a non existent file"

tests/source.vars

@@ -0,0 +1,4 @@
+export VAR=value
+export ARR=(1 2 3)
+declare -A ASSOC_ARR
+export ASSOC_ARR=([a]=AAA [b]=BBB)