CRAN release for v0.4.0

[yitao-li]

Prepare for release:

• devtools::check()
• devtools::check_win_devel()
• rhub::check_for_cran()
• rhub::check(platform = 'ubuntu-rchk')
• rhub::check_with_sanitizers()
• revdepcheck::revdep_check(num_workers = 4)
• Polish NEWS
• Polish pkgdown reference index

Submit to CRAN:

• usethis::use_version()
• Update cran-comments.md
• devtools::submit_cran()
• Approve email

Wait for CRAN...

• Accepted tada
• usethis::use_github_release()
• usethis::use_dev_version()