Lxml dependency makes wagtail-wordpress-import hard to use for windows users

[weholt]

Tried to install the latest version of wagtail-wordpress-import and it fails when trying to build lxml. I've tried installing binary versions of lxml, but nothing works.

  error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.29.30133\\bin\\HostX86\\x64\\cl.exe' failed with exit code 2
  *********************************************************************************
  Could not find function xmlCheckVersion in library libxml2. Is libxml2 installed?
  *********************************************************************************
  [end of output]

note: This error originates from a subprocess, and is likely not a problem with pip.
ERROR: Failed building wheel for lxml
Running setup.py clean for lxml
Failed to build lxml
ERROR: Could not build wheels for lxml, which is required to install pyproject.toml-based projects