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_decode_tests.h b/test/qcbor_decode_tests.h
index e87490e..7c8c185 100644
--- a/test/qcbor_decode_tests.h
+++ b/test/qcbor_decode_tests.h
@@ -38,7 +38,8 @@
 /*
  Notes:
 
- - All the functions in qcbor.h are called once in the aggregation of all the tests below.
+ - All the functions in qcbor_decode.h are called once in the aggregation
+   of all the tests below.
 
  - All the types that are supported are given as input and parsed by these tests