Split number decoding into a separate file (#276)

* Split number decoding into a separate file

* stragglers

* split out numbers header file too

* Big re ordering of functions

* Fix ifdef fan out

---------

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/example.c b/example.c
index c489ad6..473e989 100644
--- a/example.c
+++ b/example.c
@@ -16,6 +16,7 @@
 #include "qcbor/qcbor_encode.h"
 #include "qcbor/qcbor_decode.h"
 #include "qcbor/qcbor_spiffy_decode.h"
+#include "qcbor/qcbor_number_decode.h"
 
 
 /**