Accessibility features

[brlec]

The initial design was not really done in line with design principles for accessibility. I think the package should try to implement at least the bare minimum.
The following changes would probably be good to have:

• default plots are in colour schemes safe for all types of colourblindness
• increase the font size across all plots
• add the alt text descriptions to all figures used in the tutorials (i don't think you can add them to metadata of images as you make them but would be well nice if we could)
• improve the descriptions of modules to make them clearer
• no large blocks of text in the tutorials/readme
• make sure the module names are distinguishable from each other and descriptive