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.
Merge branch 'master' of https://github.com/scottransom/presto

Conflicts:
	lib/python/sifting.py
Add a python module for reading filterbank file.
Try to reduce memory usage of 'injectpsr.py'. Cherry-picked modifications to 'filterbank.py' from Patrick's commit
Modify 'filterbank.py' to use memmap numpy arrays. Cherry-picked only changes to 'filterbank.py' from Patrick's commit.

Conflicts:

	lib/python/injectpsr.py
Add ability to append spectra to filterbank format files via python FilterbankFile objects.
Check if FilterbankFile is writable.
Fix function to create filterbank files in 'filterbank.py'
Fix bug where spectra were not being cast from float64 to the appropriate dtype. Cherry-picked only changes to 'filterbank.py' from Patrick's commit.
'create_filterbank_file' function returns a FilterbankFile object of the newly created file in read-write mode.
Reduce number of times file is opened.
Add python script to convert psrfits files to sigproc filterbank format.
Continue if telescope or backend are not recognized in 'psrfits2fil.py'.
Made more general by not assuming that the 'SUBINT' hdu is the first secondary hdu.
Added support for files with > 4bit values.
Fixed typo in 'psrfits2fil.py'