cache pygments load (samuelcolvin#96)

* cache pygments load

* fix cache import

* linting

* replace "nocover"

update history

compatibility with python 3.8.6 (samuelcolvin#74)

* compatibility with python 3.8.6, fix samuelcolvin#73

* uprev

fix badges in readme

uprev

implement support for __pretty__ (samuelcolvin#36)

* implment support for __pretty__

* fix tests, use dict

* uprev

* fix intermittent timing test

update history

tweak examples, update readme

remove mypy, extend pyup interval

correct demo