Add GetSimple, update Simple Value documentation (#236)

Add the method QCBORDecode_GetSimple().  Update testing and documentation for simple values.


* Add GetSimple

* Finish off GetSimple and friends

* Fix tests when tags are disabled

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Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/test/run_tests.c b/test/run_tests.c
index a600731..d1d49ed 100644
--- a/test/run_tests.c
+++ b/test/run_tests.c
@@ -85,7 +85,7 @@
     TEST_ENTRY(IndefiniteLengthArrayMapTest),
     TEST_ENTRY(NestedMapTestIndefLen),
 #endif /* QCBOR_DISABLE_INDEFINITE_LENGTH_ARRAYS */
-    TEST_ENTRY(ParseSimpleTest),
+    TEST_ENTRY(SimpleValueDecodeTests),
     TEST_ENTRY(DecodeFailureTests),
     TEST_ENTRY(EncodeRawTest),
     TEST_ENTRY(RTICResultsTest),