Obs -> Corr (meff and dec_const_pcvc return Vector{uwreal})
2 linear_fit methods added

dec_const_pcvc is completed, new methods, Corr->Obs, Obs constructors added,  L normalization

juobs_obs added,   meff and plat_av moved to juobs_obs, Corr now includes y0,  syntax simplified(Symbol), Plots->PyPlot, LatexString support