Adds special case for degree 1 polynomial in polyfit.c as it seems that it's really only called with degree=1. Speeds up plotting and fourier analysis, for example, running "examples/transient-noise/noise_vnoi.cir" in batch mode goes from 6.7s to 5.4s.
Does it need similar error checking as in the original code? Everything seems to be working correctly right now, but there might be some corner cases.
Currently 1/f noise generator is initialized at startup even if it's not used. Initialization can be done in 1-f-code.c. Saves small amount of memory and few instructions, nothing dramatic.