Feature/apdu null length returned (#285)

* Add APDU as NULL to get BACnet type lengths.

* Fix bacapp copy test to succeed

* fix BACnet REAL and DOUBLE decode

* Add unit test for NULL APDU encoding for length

* Add unit tests for bacapp context

* refactor host-n-port to hostnport.c module

* fix BVLC decoder

* additional unit testing for bacapp

* include bacdevobjpropref module in builds

* simplify bacapp snprintf to be able to return length

* adjust compiler for variable-length arrays

* fix bug found by scan-build

Authored-by: Steve Karg <skarg@users.sourceforge.net>

ports/xplained/bname.c

@@ -166,7 +166,7 @@ bool bacnet_name_write_unique(uint16_t offset,
     bool status = false;
     size_t length = 0;
     uint8_t encoding = 0;
-    int duplicate_type = 0;
+    BACNET_OBJECT_TYPE duplicate_type = 0;
     uint32_t duplicate_instance = 0;
 
     length = characterstring_length(char_string);