Added extra PATH support (via `flake8.PATH`)
(Almost) real-time linting.

- Lint on editor buffer rather than file.
- Throttle linter calls in a small period of time.
- Call linter on content modified and saving.
- Properly clear and display errors on gutter.
process.env.PATH as PATH fallback
fix resetState when no error
Merge pull request #2 from pyrocat101/master

Improvements