Add format-independent options noDefaults and plain, which control the loading of theme witiko/markdown/defaults

[Witiko]

In PRs #373 and #392, we separated the default token renderer definitions into a universal theme witiko/markdown/defaults. In LaTeX, we can prevent the execution of the default definitions for LaTeX and only load the default definitions for plain TeX using the LaTeX option plain. However, there is no option to prevent loading any definitions altogether. Furthermore, the option plain is not available for other formats based on plain TeX such as ConTeXt.

Tasks

• Move the LaTeX option plain from LaTeX to plain TeX and react to it from ConTeXt theme witiko/markdown/defaults.
• Add new plain TeX option noDefaults and react to it from plain TeX and LaTeX.

Examples

Option noDefaults

Plain TeX example

A plain TeX document that prevents the theme witiko/markdown/defaults from being loaded.

\def\markdownOptionNoDefaults{true}
\input markdown
\markdownBegin
Hello *world*!
\markdownEnd
\bye

Expected output: Hello !

LaTeX example

A LaTeX document that prevents the theme witiko/markdown/defaults from being loaded.

\documentclass{article}
\usepackage[noDefaults]{markdown}
\begin{document}
\begin{markdown}
Hello *world*!
\end{markdown}
\end{document}

Expected output: Hello !

ConTeXt example

A ConTeXt document that prevents the theme witiko/markdown/defaults from being loaded.

\def\markdownOptionNoDefaults{true}
\startluacode
local kpse = require("kpse")
kpse.set_program_name("luatex")
\stopluacode
\usemodule[t][markdown]
\starttext
\startmarkdown
Hello *world*!
\stopmarkdown
\stoptext

Expected output: Hello !

Option plain

LaTeX example

A LaTeX document that prevents the plain TeX part of theme witiko/markdown/defaults from being loaded.

\documentclass{article}
\usepackage[plain]{markdown}
\begin{document}
\begin{markdown}
- foo
- bar
- baz
\end{markdown}
\end{document}

Expected output: foobarbaz

ConTeXt example

A ConTeXt document that prevents the plain TeX part of the theme witiko/markdown/defaults from being loaded.

\def\markdownOptionPlain{true}
\startluacode
local kpse = require("kpse")
kpse.set_program_name("luatex")
\stopluacode
\usemodule[t][markdown]
\starttext
\startmarkdown
- foo
- bar
- baz
\stopmarkdown
\stoptext

Expected output: foobarbaz