split qcbor.h into four separate headers (#34)

This is to make it much easier to read the header files.

Backwards compatibility with qcbor.h is retained, but use of qcbor/qcbor_encode.h and qcbor/qcbor_decode.h is preferred now.

Signed-off-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/test/qcbor_encode_tests.c b/test/qcbor_encode_tests.c
index 638a9b9..1e91378 100644
--- a/test/qcbor_encode_tests.c
+++ b/test/qcbor_encode_tests.c
@@ -30,7 +30,8 @@
 IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  =============================================================================*/
 
-#include "qcbor.h"
+#include "qcbor/qcbor_encode.h"
+#include "qcbor/qcbor_decode.h"
 #include "qcbor_encode_tests.h"