Fix tempdir problem. Fixes #25.
Prepare for release.
Fix the build under the new testthat version. Fixes #26

* Migrate to new recommended test file structure.
* Fix testing of `.libPaths()` update. `expect_match` has been replaced
with an equivalent `expect_true`
Merge pull request #27 from yoni/testthat-upgrade

Testthat upgrade and prepare for release.