Version 0.1.1: Moved to ROpenSci, GPL-2

• Transferred repo ownership to ropenscilabs
• The license was changed from MIT to GPL-2. This is based on the realization that the catalog data is licensed under the GPL, and the package includes a processed version of the catalog data. (See here).
• Updated datasets to 5/5/2016 and added a "date_updated" attriute to tell when they were last updated
• Added all_languages and only_languages arguments to gutenberg_works, allowing fine-grained control of languages. (For example, "either English or French" or "both English and French")
• Changed get_gutenberg_mirror to use xml2 directly, in order to handle AppVeyor
• Removed use of data() in gutenberg_works, since it slows down gutenberg_works about 2X
• Various documentation, vignette, and README adjustments in response to ROpenSci feedback.
• Added AppVeyor for Windows continuous integration
• Added code coverage information through codecov.io and covr, along with tests to improve coverage