t2t.lang: Use markup styles
This also updates the test file with content from https://raw.githubusercontent.com/txt2tags/txt2tags/v2/samples/sample.t2t (linked from https://txt2tags.org/sample.html).
This also updates the test file with content from https://raw.githubusercontent.com/txt2tags/txt2tags/v2/samples/sample.t2t (linked from https://txt2tags.org/sample.html).