Added findStringInstance function to strings package

packages/strings/strings.grnd

@@ -82,4 +82,41 @@ fun -string !matchStart -string &str -string &instr
     call !mid &store
     equal $store $instr &store
     return $store
+endfun
+
+fun -int !findStringInstance -string &str -string &instr -int &instance
+    getstrsize $instr &len
+    subtract $len 1 &len
+    set &idx $len
+
+    @loop
+        set &tempstr ""
+        subtract $idx $len &tempidx
+        subtract $tempidx 1 &tempidx
+        @subloop
+            equal $tempidx $idx &store
+            if $store %continue
+            add $tempidx 1 &tempidx
+
+            getstrcharat $str $tempidx &store
+            add $tempstr $store &tempstr
+            jump %subloop
+
+
+        @continue
+        equal $tempstr $instr &store
+        if $store %decrement
+        add $idx 1 &idx
+        jump %loop
+    
+        @decrement
+        equal $instance 0 &store
+        if $store %end
+        subtract $instance 1 &instance
+        add $idx 1 &idx
+        jump %loop
+
+    @end
+    subtract $idx $len &idx
+    return $idx
 endfun