Stable release for v4.0.0

[motss]

TO-DO list

Done

• [x] Jumping table caption in Safari. See Webkit bug. (cb122ab)
• [x] disabledDays disables dates that do not fall in the defined weekdays.
• [x] No autofocus when first render. User can choose to focus on the first focusable element by listening to datepicker-first-update event. (200d0f0)
• [x] tabindex does not update accordingly to focused date
• [x] Update demo with latest changes
• [x] To add alwaysResetValue (#176)
• [x] When there is no focused date in current calendar month, keyboard key is not able to focus on calendar day since all are tabindex="-1" set
• [x] Provide minimal customization on scrollbar thumb in year list view (#173)
• [x] Update TypeScript to 3.8 for import type from '...'
• [x] Improve accessibility with VoiceOver (macOS) and NVDA (Windows). Inspired by Angular Datepicker and ARIA: grid role
• [x] Fix mouseleave not being handled (#174)
• [x] Support ::part in datepicker dialog
• [x] Update tests and docs with available parts
• [x] Initial support for ::part, which has been supported in stable Chrome and Firefox. See ::part()
• [x] Fix calendar day not having consistent width thus content not being centered (#169, #172)
• [x] Add --app-datepicker-focused-year-bg-color (#170)
• [x] Update doc for mwc-dialog integration
• [x] Shoutout to awesome-lit-html resources to feature this element
• [x] Update app-datepicker-dialog to include 2 new buttons: Clear and Set (#161)
• [x] Include demo to integrate with mwc-dialog
• [x] Fix broken table in documentation
• [x] Update disabled day's default color in CSS Properties section

Not under consideration

• [ ] Add tests for mwc-dialog integration

[motss]

ETA: March 15, 2020 Found a critical bug when updating disabledDays with showWeekNumber set to true.

ETA: March 18, 2020 Delayed until further notice due to https://twitter.com/polymer/status/1240405092605595648

ETA: April 1, 2020

[motss]

📦 Released v4 at 2a66af13acf62231630139b5e7664ac48f13812e. Closing this happily! 👍