/*
 * call-seq:
 *    uncompress(data)
 * Decompress a string of bz2 compressed data.
 *
 *    Bzip2.uncompress Bzip2.compress('asdf') # => 'asdf'
 *
 * @param [String] data bz2 compressed data
 * @return [String] +data+ as uncompressed bz2 data
 * @raise [Bzip2::Error] if +data+ is not valid bz2 data
 */
static VALUE bz_uncompress(int argc, VALUE *argv, VALUE obj) {