Spellcheck, fix docs for R CMD check, rebuild pkgdown

[alistaire47]

Hi! Saw a typo on the pkgdown, figured I'd make a quick PR, and things escalated to a bit more housekeeping-type stuff. I see there are some similar PRs already, but they're years old and would need a messy rebase and update, so I figured it's easier just to start from scratch. If this PR gets to be that old, feel free to decline it.

What this does:

1. Spellchecked docs
2. Tweaked docs where necessary to make R CMD check pass a. One notable change here is deprecating the smart param of ipsum(), because it gets passed to rmarkdown::html_document_base() which is ignoring it. Can handle this differently if you like, but it had to be documented somehow for R CMD check to pass.
3. Rebuilt pkgdown site to capture all the updates to docs a. I did add a truly minimal _pkgdown.yml with the URL linked from this repo (https://cinc.rud.is/web/packages/hrbrthemes/), though it looks like it's also hosted on gh pages (https://hrbrmstr.github.io/hrbrthemes/). That file can be reverted or changed if desired.