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>

apps/gateway/Makefile

@@ -1,14 +1,8 @@
-#Makefile to build BACnet Gateway Demonstration Application for the Linux Port
-
-# tools - only if you need them.
-# Most platforms have this already defined
-# CC = gcc
+#Makefile to build BACnet Application using GCC compiler
 
 # Executable file name
 TARGET = bacgateway
-
-TARGET_BIN = ${TARGET}$(TARGET_EXT)
-
+# BACnet objects that are used with this app
 BACNET_OBJECT_DIR = $(BACNET_SRC_DIR)/bacnet/basic/object
 SRC = main.c \
 	$(BACNET_OBJECT_DIR)/gateway/gw_device.c \
@@ -54,6 +48,9 @@ BACNET_BASIC_SRC = \
 	$(BACNET_SRC_DIR)/bacnet/basic/tsm/tsm.c \
 	$(wildcard $(BACNET_SRC_DIR)/bacnet/basic/service/*.c)
 
+# TARGET_EXT is defined in apps/Makefile as .exe or nothing
+TARGET_BIN = ${TARGET}$(TARGET_EXT)
+
 SRCS = $(SRC) $(BACNET_SRC) $(BACNET_BASIC_SRC) $(BACNET_PORT_SRC)
 
 OBJS += ${SRCS:.c=.o}