.markdown instead of .text as file extension

[aslakr]

I guess the use «.text» instead of «.markdown» is for historical reasons, since the original
MarkdownTest used it, but wouldn't it be more practical to use .markdown today?

[michelf]

It's not just historical. Other test suites are based on MarkdownTest and use ".text" too, so I'd tend to keep it as it is for interoperability reasons. We don't gain much by changing the extension do we?

[jirutka]

Why not widely used .md? It’s more pragmatic as a file extension than a horribly long .markdown.