Implement loading XML/JSON templates from files

[mschatten]

APi/APi.g4

Lines 63 to 67 in e1208c0

	/* TODO: Nice to have feature would be to be able to load
	a JSON or XML template from a file, instead of
	writing it into the production rule, i.e. something
	like:
	json load "template1.json" > xml load "template1.xml" */