Split filter() into two functions

[tbrown122387]

Consider rewriting filter() so that it makes use of two public functions: one to perform mutation and rewrighting, and the other to perform resampling. This added level of control would be useful for latency-sensitive applications that only need to make use of the results from the first stage. After that, resampling could be performed while there is plenty of downtime.

A challenge would be to ensure that a.) one cannot use both schemes simultaneously, and that if one opted for the more involved scheme, that errors would be thrown when the ordering was broken.

Or perhaps this would best be done with two separate class templates.