Fix enum conversion warnings for LLVM/XCode 11 (#44)

* Fix enum conversion warnings for LLVM/XCode 11

* Add int conversion warning back in to optional CFLAGS

* type conversion and integer overflow fix when decoding maps as arrays

* add test for map that is too large to handle as an array

Co-authored-by: Laurence Lundblade <lgl@securitytheory.com>
diff --git a/Makefile b/Makefile
index b9feabd..543342f 100644
--- a/Makefile
+++ b/Makefile
@@ -15,7 +15,7 @@
 # The following are used before a release of QCBOR help to make sure
 # the code compiles and runs in the most strict environments, but not
 # all compilers support them so they are not turned on.
-#CFLAGS=-I inc -I test -Os -fpic -Wall -pedantic-errors -Wextra -Wshadow -Wparentheses -xc -std=c99
+#CFLAGS=-I inc -I test -Os -fpic -Wall -pedantic-errors -Wextra -Wshadow -Wparentheses -Wconversion -xc -std=c99
 
 
 QCBOR_OBJ=src/UsefulBuf.o src/qcbor_encode.o src/qcbor_decode.o src/ieee754.o src/qcbor_err_to_str.o