sparklyr.nested 0.0.3

• Initial release
• To support read schemas, array_type, binary_type, boolean_type, byte_type, character_type, date_type, double_type, float_type, integer_type, long_type, map_type, numeric_type, string_type, struct_field, struct_type, and timestamp_type are provided. These will return java references neede for schema definition.
• sdf_select enables access to nested fields (instide maps, structs, and arrays of structs).
• sdf_explode will convert arrays of structs to simple structs by duplicating rows over each unique array entry. Also works on map types if is_map=TRUE.
• sdf_nest and sdf_unnest are similar to the similarly named tidyr functions. sdf_unnest essentially chains sdf_explode and sdf_select with some schema inspection.
• sdf_schema_json and sdf_schema_viewer support schema interrogation