Fixes #84: Choice of float/double

* Can now choose between using `double` and `float` internally, for floating-point work, using the `PRINTF_USE_DOUBLE_INTERNALLY` definition and corresponding CMake option.
* Adjusted test suite to support the different choice of floating-point type:
	* Tests relevant both to `float` and `double`, but with different precisions, are adjusted with an `#if #else #endif`
	* Tests and test cases relevant only for `double` precision are not compiled at all when `float` is used.
* Lots of new explicit conversions :-(

CMakeLists.txt

@@ -21,14 +21,17 @@ option(SUPPORT_MSVC_STYLE_INTEGER_SPECIFIERS  "Support the I + bit size integer
 option(SUPPORT_WRITEBACK_SPECIFIER            "Support the length write-back specifier (%n)" ON)
 option(SUPPORT_LONG_LONG                      "Support long long integral types (allows for the ll length modifier and affects %p)" ON)
 option(ALIAS_STANDARD_FUNCTION_NAMES          "Alias the standard library function names (printf, sprintf etc.) to the library's functions" ON)
+option(USE_DOUBLE_INTERNALLY                  "Use the C `double` type - typically 64-bit in size - for internal floating-point arithmetic " ON)
 
 foreach(opt
 	SUPPORT_DECIMAL_SPECIFIERS
 	SUPPORT_EXPONENTIAL_SPECIFIERS
 	SUPPORT_MSVC_STYLE_INTEGER_SPECIFIERS
 	SUPPORT_WRITEBACK_SPECIFIER
 	SUPPORT_LONG_LONG
-	ALIAS_STANDARD_FUNCTION_NAMES)
+	ALIAS_STANDARD_FUNCTION_NAMES
+	USE_DOUBLE_INTERNALLY
+)
 	if (${${opt}})
 		set("PRINTF_${opt}" 1)
 	else()

printf_config.h.in

@@ -8,6 +8,7 @@
 #define PRINTF_SUPPORT_MSVC_STYLE_INTEGER_SPECIFIERS @PRINTF_SUPPORT_MSVC_STYLE_INTEGER_SPECIFIERS@
 #define PRINTF_SUPPORT_LONG_LONG                @PRINTF_SUPPORT_LONG_LONG@
 #define PRINTF_ALIAS_STANDARD_FUNCTION_NAMES    @PRINTF_ALIAS_STANDARD_FUNCTION_NAMES@
+#define PRINTF_USE_DOUBLE_INTERNALLY            @PRINTF_USE_DOUBLE_INTERNALLY@
 
 #define PRINTF_INTEGER_BUFFER_SIZE              @PRINTF_INTEGER_BUFFER_SIZE@
 #define PRINTF_DECIMAL_BUFFER_SIZE              @PRINTF_DECIMAL_BUFFER_SIZE@