Implement a resampling method

[Alzathar]

Currently it is possible to downsample a math::XprBase expression with an integer ratio by taking only a sample every ratio samples. However, this is not complete to create a decimation by an integer factor.

In general, it will be more interesting to implement a resampling function to be able to downsample and upsample a signal. As mentioned in this post, this resampling function would use a method similar to the resample function proposed in Scipy.