3.1.0

Development:

• Add \markdownSetup command to all TeX formats. (#275, #349, matrix.org)
• Add an optional argument to the markdown LaTeX environment. (#299, #351)
• Add support for Pandoc mark syntax extension. (jgm#67, #303, #352, matrix.org, contributed by @Omikhleia)

Deprecation:

• Deprecate the markdown* LaTeX environment. (#299, #351, matrix.org)

Unit Tests:

• Add support for YAML metadata in testfiles. (#345, #347, matrix.org)

Documentation:

• Add a link to a preprint from CSTUG Bulletin to README.md (in Czech). (2c354f4)