Add better support for continuous, non-epoched data analysis

[seqasim]

In particular, people may want to perform sliding window analyses of resting state data. In this case, my favorite approach would be to use MNE's built in tool for making fixed-length epochs (e.g. 500 ms) with an overlap/step size (e.g. 250 ms), like so:

epochs = make_fixed_length_epochs(raw=raw, duration=0.5, overlap=0.25)

This is pretty powerful as it can basically turn any epoched analysis we perform in this repo into a sliding window analysis of longer stretches of data!