[IMG124] update packaging

Zhang, Chenrequested to merge
IMG124_update_packaging into next
  • Original Gitlab Story: IMG114

This PR introduces the following changes:

  • Deprecated setup.py in favor of setup.cfg and pyproject.tmol
  • Add meta.yml for build conda package
  • Follow the standard convention by renaming python to src
  • Update git ignore list
  • Add the following info to developer documentations
    • how to release imars3d on PyPI and Conda
    • how to setup local dev environment

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