Updated build ignore list
Several fixes

- Kurt Hornik requested removing some top level files. Those are now in .RBuildignore
- Rebuilt the package under new roxygen/devtools. This required some changes to roxygen tags. Replaced @S3method with @export.

All checks pass except for this note:

* checking sizes of PDF files under ‘inst/doc’ ... NOTE
Added some unit tests
Merge pull request #10 from ropensci/cran-fix

Cran fix