Changes 1.9 -> 2.0:

- Improved handling of incomplete FITS headers by defaults
- Unified and improved blanking handling
- Removed bug in fitting function introduced in 1.9
- Increased iteration number in curvefit to obtain convergence
  in most cases
- Tried to catch exception when fit does not converge

Changes 2.0 -> 2.1:

- Better spacing of the filter sizes at large lags leading to an
  accelaration of the code for large maps
- Start of lags at sqrt(2) because of insignificance of point at 1

Changes 2.1 -> 2.2:

- Corrected error propagation in fit routines
- Work around for wrong weight treatment in curvefit without error weighing
- Changed default behaviour to "error weighing" in fit
- Added file name storage for output postscript files

Changes 2.2 -> 2.3:

- Added consistency checks to guarantee that weights map matches data
- Improved help texts
- Double treatment of beams to allow for very large maps

Changes 2.3 -> 2.4:

- fixed blanking treatment for blanks of 0.0
- switched to double accuracy for all fields to allow for large numbers

Changes 2.4 -> 2.5:
- include error handling for infinite values
- fixed bug in zero padding that wasted computer time
- Added progress output
- Increased size of all widgets
- Field plotting without contours by default

Changes 2.5 -> 2.6:
- changed padding of non-periodic fields for better factorization,
  gives major speed-up