Provides easier interaction with Socrata open data portals http://dev.socrata.com. Users can provide a 'Socrata' data set resource URL, or a 'Socrata' Open Data API (SoDA) web query, or a 'Socrata' "human-friendly" URL, returns an R data frame. Converts dates to 'POSIX' format. Manages throttling by 'Socrata'.
Closes #220
Mainly cosmetic changes to avoid any notes from CRAN.
Note there are still issues with Travis CI and Appveyor, but those shouldn't affect the submission.