Changes:
- Improved logging, e.g. support for streams
- Optional stack trace added to logging
- Full support for volume direction
- Better parsing of NRRD and NIFTI, including direction
- Math:
- Class for 3x3 matrices: Matrix3x3f
- Norm operators for float4
- Additional operators for vector fields:
- Divergence
- Rotor
- Circulation density
- Codebase is now C++11 only
- Compiles on OSX
- Various bug fixes