GitLab

* use f-string

* delete python3.5 sup

* minor fix

* fix supported python version

* fix format

* fix yapf

* remove redundant space

* fix typo

* fix a potential bug of removing temp dir

* bump version to v0.4.2

* add copyright header

* change # to // for cpp files

* add yapf and isort to travis

* minor formatting

* remove blank lines

* skip unit tests for progressbar when python2

* update travis to ubuntu 16.04

* use a newer version ffmpeg

* add -y to add-apt-repository