Create doc similar to ggplot2 aes specification page

[machow]

It appears that plotnine currently accepts 4 options for linetype, which are documented in the notes of scale_linetype().

A user mentioned that it's a bit tricky finding options for things like linetypes in the docs. One neat page on the ggplot2 docs, that helps with this challenges, is the aesthetics specifications page. This page shows the options for 5 big categories:

• color and fill
• lines
• polygons
• point
• text

Seems like it could be a helpful piece! WDYT of adding a tutorial page for it now, and then I can experiment with putting it in the guide I'm working on? I'm happy to take a stab at it, if useful!

[machow]

I'm working on a copy of this now! Will sync with Hassan on this a bit. But overall now that I'm digging deeper into it this spec doc seems super handy!