ENH: Add StataWriter 118 for unicode support

Add StataWriter with unicode support

Author: bashtage

pandas/core/frame.py

@@ -1915,14 +1915,17 @@ def to_stata(
         >>> df.to_stata('animals.dta')  # doctest: +SKIP
         """
         kwargs = {}
-        if version not in (114, 117):
+        if version not in (114, 117, 118):
             raise ValueError("Only formats 114 and 117 supported.")
         if version == 114:
             if convert_strl is not None:
                 raise ValueError("strl support is only available when using format 117")
             from pandas.io.stata import StataWriter as statawriter
         else:
-            from pandas.io.stata import StataWriter117 as statawriter
+            if version == 117:
+                from pandas.io.stata import StataWriter117 as statawriter
+            else:
+                from pandas.io.stata import StataWriter118 as statawriter
 
             kwargs["convert_strl"] = convert_strl