Add new tool for developing (lint/autopep8/isort/test)
New tool uses flake8 and isort for lint checks.
Deprecate existing tool (still works)
Update readme
Update Travis config
* Update isort settings
* Apply import sorting (isort) on all files in nyaa/
* Fixed Flake8 errors in nyaa/ (see PR for list)
* Add isort to lint.sh and requirements.txt