Allow arbitrary noise spectra/functions to be defined for op-amps, resistors, etc.
There is nothing stopping op-amps, resistors, etc. from having arbitrary noise spectra. The config file could support the standard white noise + 1/f noise parameters, or alternatively support noise spectra loaded from user files (perhaps overridden using a context manager - see #11). Such loaded files would either need to have the same frequency axis as the analysis, or be interpolated, with suitable warnings where the ranges do not overlap.