Fix CRAN build notes

Fix validation test errors due to new sort order

Use correct pattern for custom expectations

Fix broken regression tests

Fix and add test for regression

All unit tests pass with stringsAsFactors=FALSE default

Merge branch 'feature/registration' into develop

Register native code (fixed #48)

Merge branch 'feature/travis' into develop

Use APT addon

Add APT dependencies

Add Travis CI

Merge branch 'dois' into develop

Merge branch 'resolve-DOIs-securely' of https://github.com/katrinleinweber/gemtc into dois

Hyperlink DOIs against preferred resolver