simmer 4.4.6.4

New features

• Add support for activity tags via tag argument (as part of #287).
• Add support for named rollbacks via tags. The amount argument is deprecated
  in favor of the more generic name target. The former will still work, but
  raises a warning (#287 addressing #197).
• Switch to C++17, drop Boost usage (#297).

Minor changes and fixes

• Fix call identification on error (#286).
• Make tests less verbose by default.
• Fix deprecated functionality in vignette.
• Fix vignette to feed character input to numeric_version.
• Fixes for Apple Clang 10.
• Fix format-security warning.
• Fix pandoc error in JSS vignette.