Calls the formatter. Takes a ref to the content as well as the context object. Note that this is different from the format_content method of non-main formatters. This is because we don't want all main formatters to be called when iterating over pluggable modules in MojoMojo::Schema::ResultSet::Content::format_content.
main_format_content will only be called by <MojoMojo::Formatter::Main>.
Note that Text::Markdown ensures that the output always ends with one
newline. The fact that multiple newlines are collapsed into one makese sense,
because this is the behavior of HTML towards whispace. The fact that there's
always a newline at the end makes sense again, given that the output will always
be nested in a block-level element, be it a <p> (most often),
<table>, or <div> (when passing HTML through).
