fix some docs typos (r-lib#764)

Prepare for release

fixed usage section for infix functions containing <- (r-lib#569)

* fixed usage for infix with <-; fixes r-lib#554

* added NEWS bullet for r-lib#554

Prepare for release

Update vignettes

Fix indenting

Title case for title

gsub with bytes - safer on windows

Upgrade to roxygen2 4.0.1

Merge pull request r-lib#242 from PeteHaitch/patch-1

Update roxygen2.Rmd