scbs 0.6.1 - improved output of scbs diff

This minor release addresses issues #15 and #16.

scbs diff now reports a lot more information and summary statistics for each DMR, including the raw p-value, the mean methylation level in both cell groups, the number of CpG sites in the DMR, the number of cells that had sequencing coverage in each group, etc.
Both scbs diff and scbs scan now optionally write a header with the --write-header flag.
Also scbs filter no longer just throws away the log_info.txt file and instead copies it to the filtered directory, as it should.