Uses C++ via the 'Rcpp' package to parse modern Excel files ('.xlsx'). Memory usage is kept minimal by decompressing only parts of the file at a time, while employing multiple threads to achieve significant runtime reduction. Uses <https://github.com/richgel999/miniz>, <https://github.com/ebiggers/libdeflate>, and <https://github.com/lemire/fast_double_parser>.