New tutorial notebooks and improved documentation

[AdeelH]

The dev version of the documentation (https://docs.rastervision.io/en/latest/index.html) has been updated. We now have

• Some tutorial notebooks for how to use individual components of Raster Vision (https://docs.rastervision.io/en/latest/tutorials/index.html) with more on the way.
  • Note: You can run Jupyter notebooks inside the docker container by passing --jupyter or --jupyter-lab to docker/run.
• A full API reference (https://docs.rastervision.io/en/latest/api_reference/index.html).
• A new theme.

This is part of an ongoing effort to revamp the documentation in light of #1395 and #1460.

We are also nearing a new release (v0.20).

Any feedback or suggestions regarding the documentation (or anything else) are welcome.