Bugfix/add makefile lint fix warnings (#39)

* fix warnings indicated by scan-build lint tool

* add lint target to makefile using scan-build tool

* add lint into build script stages (note: uses scan-build-7)

* fix potential use of memory after it is freed

src/bacnet/readrange.c

@@ -428,7 +428,6 @@ int rr_ack_decode_service_request(uint8_t *apdu,
             decode_unsigned(&apdu[len], len_value_type, &rrdata->FirstSequence);
     }
 
-    len = apdu_len; /* There should be nothing left to see here */
     return len;
 }