Several minor changes

1. Modified all parts of the code that depended on a fixed number of
sampling points.
2. sigma factor is now 0.5
3. Extended the sampling points up to 200, sampling cutoff -> 100,
minimum matrix size -> 400x400.
introduced weighted.fitting variable

This variable controls the type of non linear fitting that is performed.
If TRUE then weights equal to the inverse of the variances of the values
being fitted are used, if FALSE ( default ) then weightless fitting is
performed instead.

Additionally, the message reporting unconverged data has been altered so
that it prints the maximum of the max.of.mins instead of the a0 of the
fitting of the max.of.mins values.
code cleanup
Reworded some comments and an error message