Additional features.

- Improved cookie support: the new --cookie-file options
  allows the reuse of a cookie across invocations of the tool;
  this allows higher query rates than would otherwise result
  when invoking scholar.py repeatedly.

- Workaround: remove the num= URL-encoded argument from parsed
  URLs. For some reason, Google Scholar decides to propagate
  the value from the original query into the URLs embedded in
  the results.