Add more user stories.
US11: Compute relative exposure

- Add relativeExposure method to compute the relative exposure between two images.
- Add computeRelExposure method to compute the relative exposure between each pair of adjacent images in a stack.
US12: Use ImageStack from GUI

- Change ExposureStack with ImageStack in MainWindow and RenderThread.
- Rename Histogram.getMedian to getPercentile.
- Rescale relative exposure of first image to 65535/max.
- Experiment with relativeExposure, not sure if improved.
- Add value() and buildOutputFileName() methods to ImageStack.
- Minor changes in README.
US10: Add Demosaic class

- Add Demosaic class, with code from LibRaw's AMaZe implementation.
US10: Add several postprocessing steps

- Rename class Demosaic by Postprocess.
- Change Image class so that it executes LibRaw::raw2image. It stores both raw and parsed data.
- Add compose and gaussianBlur methods to ImageStack, to build the composed image prior to postprocessing.
- In Postprocess class, add process, convertToRgb, moveG2ToG1 and auxiliary methods.
US10: Mark user story as still doing, to test it
US3: Save file to PFS + optimizations.

- Add savePFS method to Postprocess.
- Add a progress indicator for the save process.
- Add a merge map to speed up ImageStack.
- Add MergeMap class with fast blur algorithm.
US3: Change output color space to XYZ, start WB

- Change final colorspace to XYZ, needed by psf and Tiff LogLuv.
- Add white balance methods and data to Postprocess, from LibRaw. Not working yet.
- Add alternative invocation, without gui, to automate load-process-save procedure.
US3: Add Tiff save method

- Add saveTiff method to Postprocess, to save in TIFF LogLuv format.
US3: Try to add a an EXIF tag to a TIFF file (not working)
General optimizations

- Remove unused Exposure* classes.
- Revert to previous Image layout, without the dcraw image field.
- Correct black subtraction.
Optimizations.

- Improved relative exposure with integer math.
- Added OpenMP support, not in use yet.
Add new user story to save to DNG Float
US16: Add support for Adobe DNG SDK 1.4

- Include Adobe DNG SDK 1.4 source code in the boundle.
- Add rules to build it.
- Add instructions to build the XMP SDK.
US16: Output a DNG Float file

- Move the DNG-related definitions and includes to the root CMakeLists.txt.
- Link the main executable with the dng and xpm libs.
- Add class DngWriter, to write a DNG Float file from an ImageStack.
- Image only uses LibRaw at load time, then copies everything to MetaData.
  There are namespace collisions between LibRaw and DNG SDK.
- TODO: flip/rotate the image at load time, when the buffer is copied.
- A pixel is efectively saturated if any adjacent pixel is saturated.
  This avoids color shifts.
- Add compose method to ImageStack to build a plain float image.
- Paint pixels from different images with a different tone.
- Fix output filename creation, in ImageStack, and add test.
US16: Add an iterator-like interface to Bitmap.

- Change Position to act as an iterator.
- Modify other methods to use it.
- Start writing the saturation bitmap methods.
US16: Improve image index creation.

- Remove the or3by3 method in Bitmap, it is slower.
- Rename Bitmap::Position by Bitmap::iterator.
- Improve isSaturated with a precalculated vector of deltas.
- Improve preview color.
Fix starting GUI with preloaded files
US16: Fix Cam-XYZ matrix

- Fix loading the cam_xyz matrix. LibRaw does not load it from DNG files.
  Use its own code in adobe_cam_xyz function to load the correct values.
Remove postprocessing code, only DNG output remains