Invoke Tasks - Enable PTY on supported platforms

[calebcartwright]

I decided back in the day not to turn this on since it'd likely cause challenges on Windows, but that shouldn't preclude us from ever turning it on. Let's conditionally enable this so that it's off on Windows but otherwise on, as enabling is quite helpful on Linux/Mac as well as WSL

Here's a reference where it's always enabled (in a project exclusively targeting *nix-like envs)
https://github.com/swellaby/dotfiles/blob/8356cf7c4a27aeb306432b18430c810cab925bf7/tasks.py#L19

Would need something similar, but conditional based on the OS, on these lines in this project:

• letra/tasks.py

  Line 10 in 1920dd2

  return c.run(cmd)

• letra/tasks.py

  Line 37 in 1920dd2

  return c.run("pytest")

• letra/tasks.py

  Line 45 in 1920dd2

  return c.run("xdg-open " + path)

• letra/tasks.py

  Line 49 in 1920dd2

  return c.run("open " + path)

• letra/tasks.py

  Line 59 in 1920dd2

  return c.run("pycodestyle .")

[calebcartwright]

@marjorienorm - if you're interested in doing a little bit of Python this would be a helpful place to start 😉