separate_ratio_est: Compute ratio estimator for strata and separate ratio...
In tereom/mapacurracy: Computing map accuracies

Ratio estimator is computed for each strata and then a separate version of the ratio estimator is computed where the estimates of the strata are weighted according to the area of each stratum (unlike traditional estimator that weights with number of polygons sampled). strata_ratio_est returns the estimates for each strata in the sample (assuming SRS within strata).

1	separate_ratio_est(data, estratos_area, stratum, y, M, N)

`data`	`data.frame` each line is an observation and includes the stratum and columns used in ratio estimation.
`stratum`	unquoted column with strata in the data and allocation `data.frame`'s (the columns must have the same name in the two `data.frame`'s)
`allocation`	`data.frame` with a column defining the strata and a column with sample size allocations for each stratum (one line per stratum).
`y:`	unquoted variable in data corresponding to numerator in ratio (eg. binary vector 1 correctly classified 0 ow) #' @param M: unquoted variable in data corresponding to denominator in ratio (eg. polygon areas)
`N:`	number of polygons in the strata.