Replace RSI with SIR everywhere

[msberends]

SIR is the common tri-form. Since we hit 2.0 soon, this is the (only) moment to make such a move.

Make sure to run through NAMESPACE to keep all old functions too, but usage must return a warning once per session.

# old RSI functions
S3method("[<-",rsi)
S3method("[[<-",rsi)
S3method(as.rsi,data.frame)
S3method(as.rsi,default)
S3method(as.rsi,disk)
S3method(as.rsi,mic)
S3method(barplot,rsi)
S3method(c,rsi)
S3method(droplevels,rsi)
S3method(mean_amr_distance,rsi)
S3method(plot,rsi)
S3method(print,rsi)
S3method(rep,rsi)
S3method(summary,rsi)
S3method(unique,rsi)
export(NA_rsi_)
export(as.rsi)
export(facet_rsi)
export(geom_rsi)
export(ggplot_rsi)
export(ggplot_rsi_predict)
export(is.rsi)
export(is.rsi.eligible)
export(labels_rsi_count)
export(n_rsi)
export(random_rsi)
export(rsi_confidence_interval)
export(rsi_df)
export(rsi_interpretation_history)
export(rsi_predict)
export(scale_rsi_colours)
export(theme_rsi)