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/basic/sys/bigend.h

@@ -24,6 +24,8 @@
 #ifndef BIGEND_H
 #define BIGEND_H
 
+#include "bacnet/bacnet_stack_exports.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
@@ -44,6 +46,7 @@ extern "C" {
 /* x[2] = 0x03 */
 /* x[3] = 0x04 */
 
+    BACNET_STACK_EXPORT
     int big_endian(
         void);