; find a specific HL7 segment in an array
; input -- ARRAY ---- an HL7 array
; input -- SEGMENT -- three-letter HL7 segment identifier
; input -- I -------- index of the found segment (or null)
; output - I -------- index of the found segment (or null)
; output - X -------- string of fields sans segment identifier
; return - HIT ------ flag indicating segment found