Release styler 1.4.0

[lorenzwalthert]

We have a new CRAN release coming up 🥳 See NEWS.md for new features. Closes #756.

Todo: Help @pat-s update his fork before/after releasing.

Prepare for release:

• devtools::check_win_devel()
• rhub::check_for_cran()
• revdepcheck::revdep_check(num_workers = 4)
• Polish NEWS
• If new failures, update email.yml then revdepcheck::revdep_email_maintainers()

Perform release:

• Create RC branch (for bigger releases)
• Bump version (in DESCRIPTION and NEWS)
• devtools::check_win_devel() (again!)
• devtools::submit_cran()
• pkgdown::build_site()
• Approve email

Wait for CRAN...

• Tag release
• Merge RC back to master branch
• Bump dev version
• Write blog post
• Tweet
• Add link to blog post in pkgdown news menu

Template from r-lib/usethis#338

[codecov-io]

Codecov Report

Merging #755 (0cbdff1) into master (a8feea9) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #755   +/-   ##
=======================================
  Coverage   90.56%   90.56%           
=======================================
  Files          47       47           
  Lines        2395     2395           
=======================================
  Hits         2169     2169           
  Misses        226      226           

Impacted Files	Coverage Δ
R/rules-line-breaks.R	100.00% <ø> (ø)
R/style-guides.R	99.39% <ø> (ø)
R/set-assert-args.R	92.30% <0.00%> (ø)

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