The SuperMemo XML importer assumed that the A-factors used by
SuperMemo map 1-1 with E-factors (which correspond to Ease in
Anki). This resulted in too large E-factors for imported items.
This change adds an A-factor to E-factor conversion to the
importer.
When importing SuperMemo XML files, indicate to the BeautifulSoup
XML parser that the <br> tag is self-closing. This prevents it
from adding a matching </br> for every <br> tag. These extraneous
tags resulted in extra newlines in items imported from SuperMemo.
While we're at it, fix the same bug for a couple of other
self-closing HTML tags.
Not sure why the original author was converting angle brackets separately -
that code breaks the example provided in #480, but I'm not sure if removing it
will break other files.
