Fix GetArray() and GetMap() on empty maps (#318)

Also, increase tests coverage on GetItemXXX and MapSearch.

Improve documentation.


* Fix GetArray() and GetMap() on empty maps

* Bring over the rest of the tests from master

---------

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/QCBOR.xcodeproj/project.pbxproj b/QCBOR.xcodeproj/project.pbxproj
index a580e4d..3e0e614 100644
--- a/QCBOR.xcodeproj/project.pbxproj
+++ b/QCBOR.xcodeproj/project.pbxproj
@@ -161,7 +161,7 @@
 		0FA9BEBC216DE31700BA646B /* UsefulBuf_Tests.c */ = {isa = PBXFileReference; fileEncoding = 4; indentWidth = 3; lastKnownFileType = sourcecode.c.c; name = UsefulBuf_Tests.c; path = test/UsefulBuf_Tests.c; sourceTree = "<group>"; tabWidth = 3; };
 		E7180F222CF1657A00513186 /* qcbor_number_decode.c */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.c; name = qcbor_number_decode.c; path = src/qcbor_number_decode.c; sourceTree = "<group>"; };
 		E7180F242CF2390100513186 /* qcbor_number_decode.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = qcbor_number_decode.h; path = inc/qcbor/qcbor_number_decode.h; sourceTree = "<group>"; };
-		E7180F252CF8F2EB00513186 /* qcbor_spiffy_decode.c */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.c; name = qcbor_spiffy_decode.c; path = src/qcbor_spiffy_decode.c; sourceTree = "<group>"; };
+		E7180F252CF8F2EB00513186 /* qcbor_spiffy_decode.c */ = {isa = PBXFileReference; fileEncoding = 4; indentWidth = 3; lastKnownFileType = sourcecode.c.c; name = qcbor_spiffy_decode.c; path = src/qcbor_spiffy_decode.c; sourceTree = "<group>"; tabWidth = 3; };
 		E7180F272CF917D200513186 /* decode_nesting.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = decode_nesting.h; path = src/decode_nesting.h; sourceTree = "<group>"; };
 		E7180F282CFCE9B000513186 /* qcbor_main_decode.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = qcbor_main_decode.h; path = inc/qcbor/qcbor_main_decode.h; sourceTree = "<group>"; };
 		E7180F292CFCE9F800513186 /* qcbor_decode.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; name = qcbor_decode.h; path = inc/qcbor/qcbor_decode.h; sourceTree = "<group>"; };