ISBN: allow for bare ISBN entry.

We'll trigger if there are at least 10 digits plus spaces and dashes
in a row.

Then clean it up and see if we can find just 10 or 13 digits in a row
which pass check digit verification.  If so, we rock on.
ISBN: support ISBN-10 with X for check digit.

X represents 10, which is a possible result mod 11.
add missing semicolon to attribution, comment out empty category and topic
templates: add more guidance information.

- Fix double-secret commenting `# #`
- Explicity label both category and topics to be completed with a link
  to appropriate section of the meta data docs
- Request tests for example queries and some negative samples.
templates/Example.pm: down with tabs.
Merge pull request #1182 from duckduckgo/zaahir/template-fix

add missing semicolon to attribution, comment out empty category and topic
ISBN: allow for as few as 9 digits with X to trigger.

In a rarely seen twist, the comment was right and the code was wrong!
Merge pull request #1180 from mwmiller/bare_isbn

ISBN: allow for bare ISBN entry.