Fast reverb for data augmentation

[desh2608]

Currently, Lhotse supports reverberating a cut/recording by explicitly providing a room impulse response (see CutSet.reverb_rir()). We can have an alternate functionality that generates a room impulse response on-the-fly, using the following method: https://github.com/yluo42/FRA-RIR.

Basically, this is an approximation of the image source method which is widely used to simulate RIRs. Because of the approximations, it is fast even when computing on CPU. This would be useful for on-the-fly augmentation in the data-loaders.

[pzelasko]

Great idea!

[desh2608]

Implemented in #799. Note that at the moment, the method does not support simulation of multi-channel arrays.