Add new plotting functionality to 'sifting.py'.
Add an attempt at making a fancy, split-scale plot.

The better approach for doing this is by creating a custom scale.
Modify harmonic scrubbing to be more exacting.

The tolerance for two frequencies to be considered the same changes with harmonic number.

Also, added information about which harmonic a candidate is to the candidate's note. This information appears in the *.accelcands.report file.
Bugfix: was returning None instead of empty Candlist
Add split log-linear scale for when periods are used on the x-axis.
Fix typo in note for short-period bad cands.
Try to fix coordinates shown in interactive display.
Modify 'sifting.py' to make it less memory hungry.
Add sigma to accelcand hits.

Update output text file's format accordingly.
When checking for DM-too-low in 'sifting.remove_DM_problems(...)' consider the hit with max sigma to be consistent with how duplicates are added to candidates.

Used to consider hit with max snr, but this allowed candidates with DM < low_dm sneak through sifting.
Make Candlist class in sifting.py iterable.
Added handling of plotting zero length candlists in plot_goodbad() in sifting.py.
Made some changes to plot_goodbad() in sifting.py to be compatible with older versions of matplotlib.
Merge branch 'sifting' into scott
Tracking of bad/duplicate candidates is off by default. Added argument to 'read_candidates' to turn it on.
Merge pull request #26 from plazar/sifting

Merged Patricks sifting changes.