Update CHANGELOG

Author: jehugaleahsa

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 4.16.0 (2021-06-27)
+**Summary** - Several years ago, I was looking into the use of `IAsyncEnumerable`. I actually had some code already that would work exclusively for .NET Core App 3.0+. Now that `IAsyncEnumerable` is part is .NET Standard 2.1, I can support for additional runtimes. I officially added a .NET Standard 2.1 build. I then added additional extension methods for the `TypedReader` and `TypedWriter` classes. I also added methods to the type mapper classes that use these extension methods internally. I found various other places where I could use the extension methods, so reimplemented them where I could. This sort of code duplication actually led to some bugs recently, so I think it benefits me to consolidate as much as I can.
+
 ## 4.15.0 (2021-05-10)
 **Summary** - Recent changes to write out headers when writing multiple records only applied to the extension method `WriteAll`. However, the mapper class's `Write` methods have a similar semantic and behaved the same as before. This commit actually changes the mapper methods to call `WriteAll` under the hood, so now the same behavior will be exhibited.