Added function to remove outliers from a dose response curve; if a curve has a single outlier, elimination of this outlier could still lead to a convergent fit. Outlier removal is currently not recursive.

Current version of fitting functions work for 5-point data, and partially for 8-point data.
Commented code that cannot be used for 8-point data
First batch of modifications for data checking in 8-point data set; may be rendered obsolete by removal of outliers and na.omit directives in fit functions