Builds multiple versions of the site

[averissimo]

Closes #184

Tested on my own fork https://averissimo.github.io/shiny.telemetry/

Both with this PR (currently active on that site) and with #181

Changes description and improvements over Rhino

• Header colors were changed as white fonts had a bad score in accessibility
  • See below for accessibility score (we still fail on AAA on 65% opacity for the version number)
• Builds site for each tag in repo
• Only looks for valid versions (vX.Y.Z, vX.Y, vX, vX.Y.Z.W, ...)
  • Rejects release candidates and tags that contain non-numeric characters
• build.R clean ups directories as function calls exit
• Installs all packages required by build.R
• Color template of latest is kept over multiple versions
  • Give consistency on documentation

Definition of done

• Have you read the Contributing Guidelines?
• NEWS.md file has been updated
• Development version has been bumped (x.y.z.90XX)
• Issue has been linked with this PR (via Closing keywords or right sidebar under Development)

[averissimo]

White font