True inverse S transform inverseS added.

This version introduces a new function inverseS - the true inverse S transform from S transform results.

• Previously, the inverse of S is calculated by recoverS - reversing the window effect on the zero frequency row of the S transform output. The recoverS method has limited applications and requires a so-called elevated Gaussian window (so the reverse application of the window does not introduce 0 division error).

• The new inverseS does not require an elevated Gaussian window and does the inverse transform by recovering each frequency component at a time.