Bump the version number to 0.5.4.

Changes since 0.5.3:
- Add vtkDICOMMetaDataAdapter to simplify use of enhanced files.
- Add SetQuery to vtkDICOMParser to query while reading the file.
- Add dicomfind for summarizing files that match a query.
- Add dicomtodicom, which does enhanced-to-legacy conversion.
- Read CT gantry-tilt images with correct slice spacing.
- Include CT gantry tilt in reader's PatientMatrix.