started writing lexer after making string lib

string/docs/find/find_last.md

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+# string_FindLast
+Look for the last occurence of `needle` in `haystack` and return its index in the string. If it isn't found, return -1.
+
+## Arguments
+- haystack (string): the string to search.
+- needle (string): the substring to look for.
+
+## Returns
+index (int): the index of the last occurence of `needle` in `haystack`. If it isn't found, return -1.
+
+## Example
+### Ground
+```python
+call !string_FindLast "abcabcabc" "b" &index
+println $index # 7
+```
+
+### Solstice
+```c
+puts string_FindLast("abcabcabc", "b") // 7
+```