Consider alternatives for markdownj

[imagejan]

The markdownj project doesn't seem to be maintained very actively anymore. How about changing this plugin to use a different parser?

See this SO post for some alternatives. While pegdown is deprecated, flexmark-java seems to be a very good option.

[imagejan]

Another alternative: https://github.com/atlassian/commonmark-java (latest version 0.14.0)

This is used e.g. by @haesleinhuepf's new plugin https://github.com/haesleinhuepf/imagejmacromarkdown.