Some fixes to string. Added fprintf and String.printf. Updated boolerr example.

lib/std/core/string.c3

@@ -75,7 +75,8 @@ fn void String.chop(String this, usize new_size)
 fn char[] String.str(String str)
 {
 	StringData* data = (StringData*)str;
-	return data.chars[0..data.len - 1];
+	if (!data) return char[] {};
+	return data.chars[:data.len];
 }
 
 fn void String.append_utf32(String* str, Char32[] chars)
@@ -173,6 +174,11 @@ fn ZString String.copy_zstr(String* str, Allocator allocator = { null, null })
 	return (ZString)zstr;
 }
 
+fn char[] String.copy_str(String* str, Allocator allocator = { null, null })
+{
+	return str.copy_zstr(allocator)[:str.len()];
+}
+
 fn bool String.equals(String str, String other_string)
 {
 	StringData *str1 = str.data();