qualtRics 3.1.6

• Add fetch_distribution_history() and list_distribution_links() for more handling of distribution data, thanks to @chrisumphlett and @dsen6644 (#221, #239)

• Changed handling of literal "NA" text input from users so it is no longer converted to an R NA value thanks to @jmobrien (#244)

• Use httr::RETRY() instead of httr::VERB() in qualtrics_api_request() to implement consistent API error-handling across all of the functions in the package. They will be retried up to 3 times if there is any non-4xx error. Thanks to @chrisumphlett (#217)

• Update fetch_distributions() for changes to the Qualtrics API, thanks to @chrisumphlett (#250)