Docs: minor formatting fixes for "borrowing items" chapter

Docs: minor formatting fixes for "borrowing items" chapter

* Images need to have a trailing [] ; ideally this would contain the
  alt text for the image, but the [] is needed to make the images
  show up at all
* Since we're touching the image:: tags anyway, make the filename
  extensions consistently lower case
* Fix a processing error; a bulleted list item wrapped so that > was the
  first character on a line, which made Asciidoc angry. Easiest thing to
  do to avoid this is just to indent the wrapped lines for each bullet
  item, but we'll do the minimal thing and just indent this one line
  this time.
* Fix one instance of Word "smart quotes" having replaced ye olde single
  quotes.

Signed-off-by: Dan Scott <dscott@laurentian.ca>