elasticsearchr 0.3.1

Changed back-end to use dplyr::bind_rows as opposed to do.call(rbind) to handle NAs consistently.

elasticsearchr 0.3.0

Added support for source filtering with the select_fields function.
Added the %info% operator to be used for retreiving cluster and index information.
Added the list_indices function for retrieving a list of all available indices.
Added the list_fields function for retrieving a list of all available indices.

Refactored valid_url with the enhanced valid_connection function, based on HTTP requests to the cluster health API.

Modified all HTTP requests to have Content-Type headers for Elasticsearch 6.x compatibility;
Fixed an issue where extract_aggs_results could not handle results from base metric aggregations;
Fixed an issue where valid_url will not return TRUE when Elasticsearch port numbers are not 4 digits long;

BREAKING CHANGE: sort has been renamed to sort_on to avoid clashing with the sort function in base R;
Fixed an issue with valid_url that was causing an error on r-oldrel-windows-ix86+x86_64;
Fixed data.frame index bug - Elasticsearch Bulk API was failing when data.frame was large (>15mb); and,
Fixed an issue with search_scroll printing dots to stdout as opposed to returning them as message output.
Enhanced search_scroll such that it retrieves a maximum of 10,000 documents per-scroll to speed-up query retrieval;