Cfncli

Issues:
- Fix Python 3.6 compatibility issue introduced in `2.1.5`.

Issues:
- Fix compatibility problem with string.Template

Issues:
- Fix release issue

Issues:
- Fix json dump error caused by template contains complex types (datetime objects).

Issues:
- Fix failure when string template returns None as match object.
- supports CAPABILITY_AUTO_EXPAND

Issues:
- Fix issue caused by awcli > 1.16.77
- Fix issue that a plain '$' will accidentally match the cross stack reference patten

Features:
- Print changeset execution note before actually calling boto3
- Colorize changeset replacement so user get alarmed when resource replacement happens