Release Urgency

[LucidOne]

I'm looking at building a conversion tool to generate Debian packaging changelogs, however the current KaC format does not have a means of noting the importance of updating to a given release. Aside from inference based on the Security change type.

Perhaps something like

...
## [1.0.0] - 2017-06-20 - Urgency: low
### Added
...

or

...
## [1.0.0] - 2017-06-20
Urgency: low
### Added
...