ENH: GateFilter available for 4DD

[kirknorth]

Adding the ability to input a radar GateFilter when dealiasing Doppler velocities with the James et al. (2001) 4-D algorithm. Note that certain kwargs are now deprecated (e.g., extra_prep) but I'll let @jjhelmus decide if these kwargs should be permanently removed or kept for backwards compatibility.

[jjhelmus]

This is great @kirknorth! I think deprecating a number of the parameters in this function makes sense and will make the gatefilter the only method for filtering gates prior to applying the 4-D algorithm. Marking the following parameters as depreciated and removing them after the next release of Py-ART is reasonable:

• extra_prep
• ncp_min
• rhi_min
• ncp_field
• rhv_field

In additional the following parameters can also be Depreciated if the _fourdd_interface file is adjust as needed. Reflectivity filtering would then be done when creating the Gatefilter:

• refl_field
• prep
• lowdbz (not explicitly mentioned in the docs)
• highdbz (not explicitly mentioned in the docs)
• rm_missing (not explicitly mentioned in the docs)

Anyone have concerns about these changes?

[jjhelmus]

Issue #253 can also be addressed by this PR.

[jjhelmus]

@kirknorth Mind if I create a branch off this PR to remove the depreciated parameters as well as the reflectivity filtering in FourDD? I think having the gatefilter be the only method for specifying what gates are excluded is best. It will take some mucking with the Cython and C files so I think a separate branch and PR will be easier than trying to merge into this one.

[kirknorth]

Sure thing @jjhelmus! And yes I agree, I think removing all hard thresholds (e.g., min_ncp, max_refl, etc.) from Py-ART functions and instead rely on the more codified GateFilter class is the proper way to move forward.