Logbeam 0.8.0

Added

• GitHub Actions sections. The ##[group] … ##[endgroup] sections of a raw GitHub Actions log are folded
  like in GitHub, with their size and error count; the ones with errors start open. Click ▸ to open one, or
  Sections to open or close them all. A search looks inside closed sections too (#14, suggested on Reddit).
• For contributors: a contributing guide, a security policy, issue and pull request templates.

Improved

• A ##[group] or ::group:: line starts an entry of its own, so a log without timestamps doesn't carry the
  last level into the next section.