SetWorkDirAt, OpenCodeAt, fix bug there, fill more doc strings

src/basic/basic_string16.cpp

@@ -479,6 +479,22 @@ String16 SkipIdent(String16 *string) {
     return begin;
 }
 
+String16 SkipString(String16 *string) {
+    String16 saved_string = *string;
+    char16_t c = At(*string, 0);
+    String16 q = {&c, 1};
+    if (c == u'"' || c == u'\'') {
+        *string = Skip(*string, 1);
+        String16 quote = SkipUntil(string, q);
+        if (At(*string, 0) != c) {
+            *string = saved_string;
+            return {};
+        }
+        return quote;
+    }
+    return {};
+}
+
 bool MatchIdent(String16 *string, String16 expect) {
     String16 copy = *string;
     String16 ident = SkipIdent(&copy);