Bump version to 1.20.0

[JoepdeJong]

Bumping the version number to 1.20.0.

Could you also create a new tag?

[coveralls]

coverage: 97.972%. remained the same
when pulling 8d4c3bd on JoepdeJong:master
into f298742 on Knio:master.

[kamiccolo]

Would love to have EVT additions released :}