Adding AdvancedMaskingAdapter and test

[awst-baum]

This PR adds an AdvancedMaskingAdapter that can be used to mask the data from a reader based on a list of filters. The list must contain 3-tuples of filter parameter: data column to filter on, operator to use and threshold to use. Operator can either be taken from a pre-defined list (same as in MaskingAdapter) or be a user-defined callable.
We'd like to use it in QA4SM to implement complex masking for SMOS data and think that it'll be useful in pytesmo in general.

Example of SMOS filter:

filtered_reader = AdvancedMaskingAdapter(reader, [
    ('Scene_Flags', smos_exclude_bitmask, 0b00001000), 
    ('Soil_Temperature_Level1', '>=', 273), ])        

(where smos_exclude_bitmask is a user-defined function)

[wpreimes]

I think that's a good way to handle bitflags, @tracyscanlon is also is/was also working on something similar I think, maybe you can give some feedback wrt. C3S/CCI flags as well?

[wpreimes]

This is just a strictly more flexible implementation for a SelfMaskingAdapter right? Would it make sense to inherit SelfMaskingAdapter from this class to show that it basically does the same but with less options? It just might confuse people which adapter they should use if there are many similar options (many people use pytesmo just as a toolbox)...

[awst-baum]

It fills the same evolutionale niche as the SelfMaskingAdapter, yeah. Personally, I wouldn't change the SelfMaskingAdapter at all (since I only left it in for compatability). Well, maybe change it to add a deprecation warning - and then remove it some time in the future.
If we add a deprecation warning and a comment a la 'please use AdvancedMaskingAdapter instead', this should help users decide what to use.