v0.9.0

Imported release from original tag date 2022-05-13.

• Feature: Add signal handling support for SIGINT and SIGTERM.
  (#150 by @clue)

• Feature: Improve error output for exception messages with special characters.
  (#131 by @clue)

• Add new documentation chapters for Docker containers and HTTP redirects.
  (#138 by @SimonFrings and #136, #151 and #156 by @clue)

• Minor documentation improvements.
  (#143 by @zf2timo, #153 by @mattschlosser and #129 and #154 by @clue)

• Improve test suite and add tests for Dockerfile instructions.
  (#148 and #149 by @clue)