Reads observed counts of either the number of groups or the size of the
groups. The file must have only two columns. One of the columns must be
labelled P or S and the other count. It does not matter if the column names
are in upper case or not. The P column can have labels 0, 1, 2, ...
representing the observation of 0, 1, 2, or more groups. The corresponding
count column should contain a positive (non-zero) count for each number of
groups. Similarly, if the file contains S counts, then the S column can
contain labels 1, 2, ... representing the observation of 1, 2, ...
fragments in a group. Note that zeros are neither allowed, or useful, in the
file as they both simply result in log-likelihood terms of zero, and
therefore make no difference.