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.
Make Candlist class in sifting.py iterable.
Merge branch 'master' of https://github.com/scottransom/presto
Return an empty Candlist instead of None if no candidates to sift in sifting.py
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.
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.