A bunch of changes
* removed stats filter in Carpenter.callQuery() because they are needed
 to provide the correct status for POST, PUT, and DELETE requests
* added the handler for DELETE request (tested and functioning)
* restored buildQuery() utility function in handleGet(), to create SELECT
 queries without repeating so much code, and because...
* I had to move the fields filtering logic out of filterBy()
* a squel issue about table aliasing in DELETE statements made necessary a
 hacky fix checking the type of the query in filterBy(), this code should
 be removed as soon as squel developers fix the problem
code styling improvement: module-exposed functions now have their own name assigned to clarify stack traces; added two empty lines between requires and actual code