Fixed `print.download` method so that NULL records don't cause it to choke.
Keyword fixes and authorship change.
*  Added Gavin Simpson to the list of authors, moving him from contributors resolves issue #126
* Changed keywords for `compile_downloads`, `get_publication` and `param_check` to partially address #124.
Merge pull request #138 from SimonGoring/master

Working on the issues list, resolving bugs.