* Fix deprecated(moved) import
* Add util/dt typing
* Green on mypy util/dt
* Fix some errors
* First part of yping util/yaml
* Add more typing to util/yaml
"unix" timestamp is number of seconds since Jan 1, 1970 UTC.
This allows scripts that use templates to generate time
deltas in seconds if desired from state attributes such
as last_updated.
Some examples:
timestamp now is
{{ as_timestamp(now) }}
timstamp of last change is
{{ as_timestamp(states.binary_sensor.garage_door.last_changed) }}
seconds since last change is
{{ as_timestamp(now) - as_timestamp(states.binary_sensor.garage_door.last_changed) }}