Prefer `{Date,Time}.current` over `.today`/`.now`

`Date.current` and `Time.current` take `Time.zone` and
`config.time_zone` into account, falling back to `Date.today` and
`Time.now` respectively if a zone isn't set.
Use double quotes in Sass
Add note about allowing for feedback

* We've had several pull requests merged quickly
* Our contribution guidelines request a week to allow feedback