Custom template for integrating book links

[nelliemckesson]

This creates some special handling for sections that are intended to link to a book. You should be able to use this same format for sections of any level. You can include any type of content inside your section, as usual, and a final paragraph will automatically be appended to the section, linking to the book with text that corresponds to the type of book. The following attributes are required:

• .booklink
• booktype (options are: free, buy, or donate)
• link to the book, buy page, or donate page
• image of the book cover (can be either included in the repo or a url). Note that in order for it to be picked up by the toolchain, the image attribute must be formatted the same way you'd format a regular asciidoc image, including both the image:: and trailing []; see below for an example.

[.booklink, booktype="free", link=https://pip.raspberrypi.com/categories/685-whitepapers-app-notes/documents/RP-003471-WP/Using-a-DPI-display.pdf, image=image::images/simple-electronics-with-gpio-zero.jpg[]]
==== Going further

You can find more information on how to program electronics connected to your Raspberry Pi with the GPIO Zero Python library in the Raspberry Pi Press book https://github.com/raspberrypipress/released-pdfs/raw/main/simple-electronics-with-gpio-zero.pdf[Simple Electronics with GPIO Zero]. Written by Phil King, it is part of the MagPi Essentials series published by Raspberry Pi Press. The book gets you started with the GPIO Zero library, and walks you through how to use it by building a series of projects. 

See #3035

[aallan]

Thanks @nelliemckesson. Ready to merge do you think? If so I'll sit down with this later today when I get some time to flip through the docs and figure out how many times I've already done this without a template, and replace all of them with this!

[aallan]

YOLO!

[aallan]

@bjepson Free, buy, or donate covers all cases I'm presuming?

[nelliemckesson]

@aallan I'm feeling good about it, so you can merge when you're ready!

[aallan]

Cool! I'll merge now then and page through the docs later. I'll get back to you if I run into any problems!

As always, thank you!