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/esp32/readme.txt

@@ -38,6 +38,7 @@ Goto lib/stack and copy the requested files from Steve code :
 	h_whois.c
 	h_wp.c
 	iam.c
+	hostnport.c
 	lighting.c
 	memcopy.c
 	noserv.c