som-10.1.3: ChangeLog.md

# Changelog for som

10.1.3 Added SGM3.
10.1.2 Fixed a warning.
       Added SGM2.
10.1.1 Fixed a warning.
       Added more documentation.
10.0.1 Upgraded to Stackage lts-12.16.
10.0.0 Revamped to work with Stack v1.7.1.

## Unreleased changes