group pattern-* related papers (#564)

* combine clustering algo into pattern matching

* rename stringology with the pattern_ prefix

* improved the README header info for paper related to patterns

pattern_stringology/README.md

@@ -0,0 +1,21 @@
+# Stringology
+
+[Stringology](https://en.wikipedia.org/wiki/String_(computer_science)#String_processing_algorithms) refers to one of the various kinds of string processing algorithms. 
+
+
+🧭 Part of the pattern-matching group, in PWL
+
+* [Pattern Matching](../pattern_matching/README.md)
+* [Stringology](../pattern_stringology/README.md)
+
+## External Papers
+
+* [A Taxonomy of Suffix Array Construction Algorithms](http://www.cas.mcmaster.ca/~bill/best/algorithms/07Taxonomy.pdf)
+    - A great introduction to
+      [suffix arrays](http://en.wikipedia.org/wiki/Suffix_array), but
+      also a survey paper that is more than the sum of its citations,
+      clarifying the presentation of all the algorithms with a
+      unifying framework.
+
+* [Fast String Searching](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.13.9460&rep=rep1&type=pdf)
+    - This paper describes techniques to improve the performance of the [Boyer–Moore string search algorithm](https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_string_search_algorithm).