Release 4.16.2

Version 4.16.2
2021-Feb-27

• Rework the import handling to check full paths when checking
  if an proto to import has already been seen. #194
• In a verifier error, emit the faulty field as a string
  instead of as an atom to avoid hitting the system limit
  of 255 chars during the making of the error re ason. #195
• Fix spec for empty messages to work with dialyzer -Wunderspecs #196
  Also emit -dialyzer({no_underspecs, /}) on erl >= 24.
• Fix the Erlang type of string fields: change to unicode:chardata()
  from iodata() to allow for unicode code points >255. #200
  For clarity, the encoding always worked with such code points,
  it was just the field's type that was wrong.
• Fix help text when using protoc-erl.
• A few fixes for Erlang 24 (doc building and in an eunit test)