Cleaned up documentation + added function

[andybeet]

Documentation

• Expanded pullingData.rmd vignette to explain the main options
• added sample data for the vignette, documentation, and code to produce it
• fixed typos in some of the get_ functions
• expanded readme.rmd to outline who this package is for
• changed maintainer of package to Andy Beet
• expanded get_survdat_data.r documentation to explain all of the fields returned

Code

• added check_argument_validation function to stop the data pull if some of the arguments would cause an error to be thrown later on in the pull

[sgaichas]

looks great Andy, thank you. The package and pkgdown website all build for me.