added changelog file

Author: jricher

CHANGELOG.md

@@ -0,0 +1,20 @@
+Unreleased:
+- Added changelog
+
+*1.3.1*:
+- Added End Session endpoint
+- Fixed discovery endpoint
+- Downgrade MySQL connector dependency version from developer preview to GA release
+
+*1.3.0*:
+- Added device flow support
+- Added PKCE support
+- Modularized UI to allow better overlay and extensions
+- Modularized data import/export API
+- Added software statements to dynamic client registration
+- Added assertion processing framework
+- Removed ID tokens from storage
+- Removed structured scopes
+
+*1.2.6*: 
+- Added string HEART compliance mode