new options to dump declaration for an extension or UTI

I've added a couple of options to duti to display the UTI declaration(s) for either an extension (-e) or UTI (-u). I hope they might be of worth to others.

The output is as follows:

    # duti -e csv
    identifier: public.comma-separated-values-text
    description: comma-separated values
    declaration: {
    	UTTypeIdentifier = public.comma-separated-values-text
    	UTTypeTagSpecification = {
    		public.mime-type = [
    			text/csv
    			text/comma-separated-values
    		]
    		public.filename-extension = [
    			csv
    		]
    	}
    	UTTypeConformsTo = [
    		public.delimited-values-text
    	]
    	UTTypeReferenceURL = http://www.ietf.org/rfc/rfc4180.txt
    	UTTypeDescription = comma-separated values
    }
    # duti -u public.delimited-values-text
    description: delimited text values
    declaration: {
    	UTTypeDescription = delimited text values
    	UTTypeConformsTo = [
    		public.text
    	]
    	UTTypeIdentifier = public.delimited-values-text
    }