Docs: create page with preprocessing examples

[danielmwatkins]

The documentation should be static, html with the example figures stored in assets. The notebook in preprocessing can provide an example of the processing routine. I'm using the matlab test images for now, but eventually aim to move the example images into the notebooks/sample_images directory.

• Land mask generation and dilation. Needs description of acceptable file types.
• Cloud mask generation. Describe what the different thresholds do and provide examples.
• Tiling and application of the adaptive histogram regularization. Potentially need to break apart sub-functions, e.g. the unsharp mask.

[danielmwatkins]

Update the logo to have a blank background

[danielmwatkins]

Image link didn't work - check documentation for Documenter