add changelog file

CHANGELOG.md

@@ -0,0 +1,56 @@
+# Changelog
+
+## [4.0.0] - 2022-01-14
+
+### Added
+
+-   `Doc` I added this CHANGELOG.md to the repo to start tracking release changes in this file rather than just in the release notes.
+A changelog file seems to be a more conventional way to easily look through changes for each release. I'm not retroactively
+adding in the previous 59 versions worth of release notes to this, but will add all future releases. 
+
+### Changed
+
+-   `BREAK` This is a breaking change, thus the incrementation of the major digit of the Sematic Version
+The change is as follows. sasdata2dataframe (sd2df or other aliases), has returned None when the SAS Data
+Set provided doesn't exist. Of course, trying to use that as a dataframe results in an exception. But, if
+you coded a check for this and conditionally didn't use it, then this change will break that code.
+A FileNotFoundError exception is now thrown, as that's the appropriate Pythonic thing to do in this situation.
+\
+If you happened to code this:
+```
+df = sas.sd2df('table','libref')
+if df is None:
+   # do something because the data set wasn't found in the SAS session
+```
+\
+Then you would need to change that to:
+```
+try:
+   df = sas.sd2df('table','libref')
+except FileNotFoundError:
+   # do something because the data set wasn't found in the SAS session
+```
+
+-   `UPDATE` Due to the continuing problems with log4j, I have to keep updating the log4j jars I include in the repo for the IOM
+Access Method (the IOM Java client requires them to be there even though they are not used). If you recently used the new `log4j`
+configuration key in the pervious release, you may will need to update the version you're specifying.
+\
+SASPy V3.7.8 had log4j 2.12.2 and 2.16.0 jars, but now 2.12.4 and 2.17.1 are included instead.
+\
+So, if you happened to use `log4j='2.16.0'`, you need to change that to `log4j='2.17.1'` in this release. Be aware
+that this can continue to change if more vulnerabilities are found and fixed in log4j.
+\
+Note also that none of the vulnerabilities are exposed by SASPy as it doesn't use log4j, so there's no actual problem with these
+regardless of their version. See more [here](https://sassoftware.github.io/saspy/configuration.html#attn-log4j-vulnerabilities-found-in-dec-2021)
+
+
+### Fixed
+
+-   `Fix` Changed a logger message from Info to Warning for the case where the SAS session encoding has no
+Python equivalent encoding to use for transcoding to/from UTF-8. Should had been Warning level, so this is now fixed.
+
+### Removed
+
+-   `None` Nothing removed
+
+