Version 0.1.1: Adding a distance column, various package management features

Features

• Added option not only to join based on a maximum distance but also to append a distance column, using the distance_col argument. This is available in difference_join, distance_join, stringdist_join, and geo_join (#10)

Bug fixes

• Fixed to ignore groups while preserving the groups of x in the output (#11)
• Fixed to append .x and .y to all common columns, not just those in by (#12)

Package management

• Added codecov to measure test coverage
• Added AppVeyor continuous integration
• Added Code of Conduct