markdownfmt makes source files unreadable

[xenophonf]

Markdown-formatted content should be readable no matter how it's presented. However, the markdownfmt CI job puts paragraphs all on one line, strips sentence-ending white space, and removes vertical whitespace, making source files difficult to navigate, read, and edit due to excessively long horizontal lines and visually indistinct sections. This also negatively impacts change reviews as edits may occur somewhere in the middle of a single line. While modern tooling like git diff --word-diff or delta can help identify mid-line edits, this isn't the default. Furthermore, those tools (and others) often rely on color-coding that's difficult to perceive for significant subsets of the population.

[tianon]

Unfortunately, one of the goals of our formatting is to deal with the differences between several markdown rendering engines (Docker Hub has switched rendering engines multiple times during the lifetime of this program/repository, for example), and semantic line breaks are not consistently rendered across all engines.

For
example,
this
should
technically
be
all
on
one
line,
but
isn't.