Markdown won't merge subsequent quoted paragraphs into a single
blockquote unless the blank line between them also has a ">" on it. Most
people don't expect this behavior when quoting a multi-paragraph
section, and end up with a bunch of separated blockquotes.
This should fix that issue by default, but still allows people to keep
their blockquotes separated by adding at least one more newline between
the two quoted paragraphs (so they have at least two blank lines), among
various other methods.