Feature/makefile add apps library (#218)

* add BACnet stack library at apps/lib

* convert apps to use apps/lib for smaller binary

* fix -DBACDL_ALL=1 build

* fix piface build

* datalink MAX_MPDU and MAX_HEADER cleanup

* add bip6 to git workflow

* fix system library dependency of BACnet library

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

.gitignore

@@ -67,3 +67,6 @@ CMakeLists.txt.user
 /out/*
 Obj/
 Release/
+apps/piface/libmcp23s17/
+apps/piface/libpifacedigital/
+