pkgdown site updates

[ddsjoberg]

Hey hey @rich-iannone !

• I moved the _pkgdown.yml file inside the pkgdown/ folder from the project root directory. This helps keep the project folder looking a bit cleaner.
• I added an authors section to the _pkgdown.yml where you can optionally list personal websites. The pkgdown site will include a link to the websites listed.

  authors:
    JooYoung Seo:
      href: "https://jooyoungseo.github.io/"
  

  
• I update the development section of the yml file. This addition will place any dev version of your website (aka has a version that contains the *.9xxx extension) into a dev/ folder. When building locally, the entire development website will live in docs/dev. When the website is pushed to a gh-pages branch, the development website will be pushed to a dev folder in the branch. Here's an example: https://github.com/ddsjoberg/ggsurvfit/tree/gh-pages/dev When you push something to the master branch and the package version number does not contain the 9000 extension, the site will be pushed the the base directory of the branch or into the docs folder when building locally. So, the package's version number determines where the site will be pushed to.

  development:
    mode: auto
    version_label: default
  

After this PR is merged, you will need to checkout the release branch from the last release and run pkgdown::deploy_to_branch() locally to build the primary website based on the last release and it will be pushed as the main website (not the dev version). If it's helpful, we can jump on a quick call tomorrow (or whenever) to discuss details!

[CLAassistant]

All committers have signed the CLA.

[rich-iannone]

I like it!