Type hints

[niklasf]

• Drop support for Python 3.4, which is now past its end of life. We can then use the typing module that was introduced in 3.5.
• Type hints:
  • core
  • polyglot
  • svg
  • variant
  • engine
  • syzygy
  • gaviota
  • pgn
• Mypy passing:
  • core
  • polyglot
  • svg
  • variant
  • engine
  • syzygy
  • gaviota
  • pgn
• Run mypy in CI
• Do not resolve aliases in documentation (Option for not unfolding aliases sphinx-doc/sphinx#6518)
• Annotate data members in documentation
• Consider newtypes

[niklasf]

Missing stdlib typings:

• AbstractChildWatcher asyncio.AbstractChildWatcher missing python/typeshed#3644
• @total_ordering @total_ordering support python/mypy#4610

[PedanticHacker]

I don't think we can tick the engine.py module as being passed by mypy just yet, because the mypy that I use spits 2 errors out:

engine.py:701: error: "BaseTransport" has no attribute "write"
engine.py:702: error: "BaseTransport" has no attribute "write"

The code in engine.py lines 699--702 is:

stdin = self.transport.get_pipe_transport(0)
assert stdin is not None, "no pipe for stdin"
stdin.write(line.encode("utf-8"))
stdin.write(b"\n")

[niklasf]

Ah, yes, the returned type of get_pipe_transport() depends on the argument. Added ignore.