Create itertools.md

Author: Joseph Luce

Diff for: pythonic/itertools.md

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+# Itertools
+This section will go over a few tools in python 3's itertools library.
+
+## count()
+
+## cycle()
+
+## repeat()
+
+## accumulate()
+
+## chain()
+
+## compress()
+
+## groupby()
+Requires that the iterable is sorted by the value you are grouping by.
+
+## dropwhile()
+
+## islice()
+
+## starmap()
+Used for when you have an iterable of iterables.
+
+```
+data = [(2,5), (1,2), (7,3)]
+for each in itertools.starmap(operator.mul, data)
+    print(each)
+
+10
+2
+21
+```
+
+## tee()
+
+## zip_longest()
+
+## combinations()
+
+## permutations()
+
+## combinations_with_replacement()
+
+## product()