Use bool from stdbool.h, get rid of BOOL

BOOL was just an alias for bool, this commit replaces all instances of it for consistency.

For some reason bool was defined as a 4-byte integer instead of a 1-byte one, presumably to match WinAPI's definition: https://docs.microsoft.com/en-us/windows/win32/winprog/windows-data-types
Nothing should break now that bool is 1-byte, as no protocol code appears to be relying on the size of the data type.
PACK, for example, explicitly stores boolean values as 4-byte integers.

This commit can be seen as a follow-up to 61ccaed4f6.

src/Cedar/Connection.h

@@ -149,7 +149,7 @@ struct UDP
 // Data block
 struct BLOCK
 {
-	BOOL Compressed;				// Compression flag
+	bool Compressed;				// Compression flag
 	UINT Size;						// Block size
 	UINT SizeofData;				// Data size
 	UCHAR *Buf;						// Buffer