Prepare for 2.1.0

Add PHP 7.4 to Travis (#12)

Prepare for 2.0.0

Prepare for 1.0.0

I do not use this in production myself yet, so it is a bit risky to do
a stable release. However it should be mature enough, and I want to
release 2.0.0 ie PHP 7 only version too.

Prepare for 0.4.0

Prepare for 0.3.0

Prepare for 0.2.3

Clean up composer config

Forgotten tag

Use the real license as header instead of a link