Add whatsnew for SDK 2.5.
Add whatsnew for SDK 2.5.

pebble/cloudpebble,pebble/cloudpebble,thunsaker/cloudpebble,math-foo/cloudpebble,math-foo/cloudpebble,thunsaker/cloudpebble,pebble/cloudpebble,math-foo/cloudpebble,math-foo/cloudpebble,pebble/cloudpebble,thunsaker/cloudpebble,thunsaker/cloudpebble,pebble/cloudpebble