Release downlit 0.3.0

[hadley]

Prepare for release:

• [x] Check current CRAN check results
• [x] Polish NEWS
• [x] urlchecker::url_check()
• [x] devtools::check(remote = TRUE, manual = TRUE)
• [x] devtools::check_win_devel()
• [x] revdepcheck::cloud_check()
• [x] Update cran-comments.md

Submit to CRAN:

• [x] usethis::use_version('minor')
• [x] devtools::submit_cran()
• [x] Approve email

Wait for CRAN...

• [x] Accepted :tada:
• [x] usethis::use_github_release()
• [x] usethis::use_dev_version()

[hadley]

Will announce with pkgdown 2.0.0.

[hadley]

Accidentally turned this into downlit 0.4.0 by running usethis::use_version('minor') twice