Lektor Pre-release of 3.1

• Added Lektor theming.
• Fix: Potential infinite build/prune loop due to pathing issue.
• Added markdown-lexer-config plugin hook.
• Fix GitHub deploy on Python 3.
• Added ability for dev shell to use IPython if it's available.
• Added ability to publish from different filesystems.
• Adding new option to turn on disabling of editing fields on alternatives.
• Added automated testing for Windows.
• Expanded automated testing environments to Python 2.7, 3.5, 3.6, & Node 6, 7, 8.
• Windows bugfixes.
• Improved exif image data.
• Improved date handling in admin.
• Make GitHub Pages branch detection case insensitive.
• Set sqlite isolation to autocommit.
• Fixed errors in the example project.
• Enabling pylint and standard.js.
• Improved image rotation.
• Now measuring tests and pull requests with code coverage.
• Thumbnails can now have a defined quality.
• Moved Windows cache to local appdata.
• README tweaks.
• Beter translations.
• Better file tracking in watcher.
• Upgraded many node dependencies.
• Upgraded from ES5 to ES6.
• Added mp4 attachment type.
• Bugfixes for Python 3.