arr_filter - use an array of function pointers to apply different filters to multiple columns

[Kiyoshika]

Currently, arr_filter supports applying the same filter to multiple columns. Want to provide functionality to apply different filters to different columns at the same time which would be more useful. Would probably have to change the function pointer to a pointer to function pointers.

In the underlying C code, could probably wrap this more complicated function around arr_filter and call it arr_filter_multiple or something like that. Then we can iterate over the array of function pointers and call arr_filter each time to modify the same array.

The method call in Python wrapper would ultimately look something like:

def filter_1(x):
    x = cast(x, POINTER(c_int32))
    return x.contents.value == 10

def filter_2(x):
    x = cast(x, POINTER(c_int32))
    return x.contents.value < 20

# apply filter_1 to column index 0
# apply filter_2 to column index 1 and 2
array filtered = arr.filter([filter_1, filter_2], [[0], [1,2]], 'ANY')

Where we can overload the filter method if the second parameter is a list of lists instead of a regular list.

[Kiyoshika]

In the C implementation, planning to call this arr_multi_filter and implement it in the filter.c file.