Release 4.17.5

Version 4.17.5
2021-May-19

• Fix generation of map types when targeting Erlang 17 and 18 (#196)

• Rework building outside of a git-repo:

  • Add the possibility to manually specify version
    by adding a gpb.vsn file.
  • Add the concept of a version source: git | file
    include this info in the generated code
  • Add a --dest-dir=DIR option to the mk-versioned-archive