keep case consistent with original project

[AndyOGo]

We shouldn't break with any unnecessary decisions made in the original project, like underscore-case used for variable names...

at the moment we need to restore the original API, like here:

json-logic-js/src/index.js

Lines 13 to 19 in 38c531d

	// restore original public API
	jsonLogic.is_logic = isLogic;
	jsonLogic.truthy = truthy;
	jsonLogic.get_operator = getOperator;
	jsonLogic.get_values = getValues;
	jsonLogic.uses_data = usesData;
	jsonLogic.rule_like = ruleLike;

and here:

json-logic-js/src/createJsonLogic.js

Lines 113 to 114 in 38c531d

	add_operation: addOperation,
	rm_operation: removeOperation,