Removed option to pass a data frame to gender function
Delete logical year functionality; refactor error checking
Vectorized by removing joins in favor of filtering

Since the data being passed in and then passed to low-level functions is now a
character vector rather than a data frame, it is no longer necessary to use
the left join method. This should make the code run faster, and it also makes
it more easily vectorized. Tests still need to be worked on.
Put single name tests into the various methods tests
Additional test for argument validation
Refactor the Kantrowitz method

Return a list or a list of lists. Allow operation on a single or multiple
names. Rewrite tests to match. Rewrite documentation.
Refactor tests
Add README image to Rbuildignore
Fixed Appveyor badge
Added git to Rbuild ignore
Updated documentation
Drop examples that use the data frame column

This is the technique that we are dropping from the package
Merge branch 'feature/drop-df' into develop
Changed examples