Export symbols in order to support shared libraries (#54)

* Add BAC_ROUTING compile definition

* Reorder cmake

* Fix OpenSSL support: support both 1.0 and 1.1t pus

* Explicitly export symbols, hidden by default

* Build shared libraries on travis using cmake

* Learn Makefile about static library

* Fix build using mingw with cmake

* Do not cleanup twice or after potential free

src/bacnet/datalink/bip6.h

@@ -16,6 +16,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 #include <stddef.h>
+#include "bacnet/bacnet_stack_exports.h"
 #include "bacnet/bacdef.h"
 #include "bacnet/npdu.h"
 #include "bacnet/datalink/bvlc6.h"
@@ -33,19 +34,25 @@ extern "C" {
     /* 6 datalink functions used by demo handlers and applications:
        init, send, receive, cleanup, unicast/broadcast address.
        Note: the addresses used here are VMAC addresses. */
+    BACNET_STACK_EXPORT
     bool bip6_init(
         char *ifname);
+    BACNET_STACK_EXPORT
     void bip6_cleanup(
         void);
+    BACNET_STACK_EXPORT
     void bip6_get_broadcast_address(
         BACNET_ADDRESS * my_address);
+    BACNET_STACK_EXPORT
     void bip6_get_my_address(
         BACNET_ADDRESS * my_address);
+    BACNET_STACK_EXPORT
     int bip6_send_pdu(
         BACNET_ADDRESS * dest,
         BACNET_NPDU_DATA * npdu_data,
         uint8_t * pdu,
         unsigned pdu_len);
+    BACNET_STACK_EXPORT
     uint16_t bip6_receive(
         BACNET_ADDRESS * src,
         uint8_t * pdu,
@@ -53,28 +60,37 @@ extern "C" {
         unsigned timeout);
 
     /* functions that are custom per port */
+    BACNET_STACK_EXPORT
     void bip6_set_interface(
         char *ifname);
 
+    BACNET_STACK_EXPORT
     bool bip6_address_match_self(
         BACNET_IP6_ADDRESS *addr);
 
+    BACNET_STACK_EXPORT
     bool bip6_set_addr(
         BACNET_IP6_ADDRESS *addr);
+    BACNET_STACK_EXPORT
     bool bip6_get_addr(
         BACNET_IP6_ADDRESS *addr);
 
+    BACNET_STACK_EXPORT
     void bip6_set_port(
         uint16_t port);
+    BACNET_STACK_EXPORT
     uint16_t bip6_get_port(
         void);
 
+    BACNET_STACK_EXPORT
     bool bip6_set_broadcast_addr(
         BACNET_IP6_ADDRESS *addr);
     /* returns network byte order */
+    BACNET_STACK_EXPORT
     bool bip6_get_broadcast_addr(
         BACNET_IP6_ADDRESS *addr);
 
+    BACNET_STACK_EXPORT
     int bip6_send_mpdu(
         BACNET_IP6_ADDRESS *addr,
         uint8_t * mtu,