mdcode: don't include blank lines at end of section.

mdcode: don't include blank lines at end of section.

completely blank lines (no indent) at the end of a section
should not be considered part of that section, but rather
separation between this and the next section.
So don't include them in the code.

When a section is used, for example, as sample output to
test against actual output in a test suit, having the
stray blank at the end can be problematic.

Signed-off-by: NeilBrown <neil@brown.name>