Migrate change log to release notes for more user focus

Author: arthompson

CHANGELOG.md

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+# Statistical methods Library 9.0.0
+
+Release date: 2022-11-29
+
+## Synopsis
+
+This release addresses various floating point accuracy issues by switching
+to the Pyspark Decimal type for all calculations where such issues may
+occur.
+
+## Changes
+
+All methods now expect columns which were previously double precision to be
+of type decimal and uses this type when outputting columns which would have
+previously been of double precision.
+
+## Notes
+
+No type casting is performed on either the input or output data frames.
+Providing columns using double precision where decimal types are now
+expected will cause an error as with any other incorrect data types.