Fix __dunder__ methods in asciidoc posts

[ramalho]

Asciidoc uses single and double underscores for italic text. Many occurrences of __dunder__ names need to be fixed in the .adoc files by replacing each _ with _, the escape code for _. For example: __dunder__. 😥

PS. The proprietary O'Reilly asciidoc toolchain doesn't use the double underscore for italic to avoid issues with __dunder__ notation, since they publish lots of books about Python. But in this site I use Asciidoctor, so this became an issue as I moved content from the book.

[ramalho]

I found a better way to fix this: replace __xyz__ with +__xyz__+. Note: in both cases we need backticks around the whole string including the + signs, to render with a fixed-width code font in asciidoc.

I've done that in several places, but if you still find dunder method names rendering as italic without the underscores, please submit a PR with the fix described in this comment. Thanks!