\* Parallelise the for-loops in `obsFiltEst()`. While execution may be slower for a small number of sources and receiver positions, the overall execution time will not increase significantly due to the functions' generally fast performance.\
\* Parallelise on of the for-loops in `obsFiltTD()`. While execution may be slower for a small number of sources and receiver positions, the overall execution time will not increase significantly due to the functions' generally fast performance.\
\* Update `obsFilt()` to return the condition of the perturbed power spectral density matrix.\
\* Update `obsFilt()` to allow a matrix of regularisation factors to be provided (it must be square and its dimensions be equal to the monitoring microphones' power spectral density matrix).\
\* Update `obsFilt()` to allow a matrix of regularisation factors to be provided (it must be square and its dimensions must be equal to the monitoring microphones' power spectral density matrix).\
\* Update `obsFilt()` to allow a matrix of SNR values to be provided (it must be square and its dimensions must be equal to the monitoring microphones' power spectral density matrix).\
\* Rename the following functions (this **breaks** backward compatibility):
