- Bring back "both" option for badge display (as requested in an AMO review)

This release includes important new features!
- Add option to count the number of windows (see GitHub issue #19)
- Add option to change badge text color for Firefox v63 and above (see GitHub issue #13)

Thank you to everyone who proposed enhancements and reported bugs through GitHub issues and Mozilla Addon reviews! This release contains bug fixes and new features!
- Add padding to popup to attempt fix for Firefox bug where popup size cuts off text (see GitHub issue #11)
- Move version check to the background script and improve it so that settings upgrade immediately
- Add new icons for dark themes and Photon styling (see GitHub issue #14)
- Remove old icon sizes and only offer PNG for clear icon (non-empty SVGs work fine in Opera v52)
- Add an option to disable live counting, badge updating, and icon hover text updating and require a click to see the count for slight performance gain (see GitHub issue #12)
- Developer Author link in Firefox addon now links to the Mozilla Addons Site Author Page
- Remove the "both" option for the counter due to the four-character badge limit (see GitHub issue #15)
- Update dependencies

- Fluid badge update for newly activated tabs once every second (see GitHub issue #6)
- Use Travis CI for building releases

- Use the tooltip of the button to show window and total counts (WebExtension badge title)
- Make popup and tooltip text consistent

New in this version:
- Fix silent (harmless) errors appearing in log
- Load WebExtension polyfill dynamically

From v0.1.1-alpha.1 (not published to AMO, see GitHub):
- More performance improvements:
- Only one timer per event
- Only run once every 250ms
- Wait five seconds after browser start

- Put icon in tab strip by default
- Drastic performance improvements
- Add option to show current window tabs, total tabs, or both
- Remove not required tabs permission

- Clean up manifest
- Use local settings storage (instead of sync)