Lots of work on unicode support

luprex/cpp/core/util.hpp

@@ -181,8 +181,14 @@ int32_t read_ascii_char(string_view &source);
 
 // Read a UTF8 codepoint from a string_view.
 //
-// If the next thing in the string_view isn't a valid
-// codepoint, returns -1 and doesn't update the view.
+// If the string_view is empty, returns -1 and doesn't update
+// the string_view.
+//
+// If the string_view contains an unfinished but possibly valid
+// codepoint, returns -1 and doesn't update the string_view.
+//
+// If the next thing in the string_view is an invalid codepoint,
+// returns -2 and doesn't update the string_view.
 //
 int32_t read_codepoint_utf8(string_view &source);