Medimages4tests

Fixes up generation of dummy NIfTI images so they aren't always just zero-filled

What's Changed
* moved append of header_vals to output dir path to generate_dicom by tclose in https://github.com/Australian-Imaging-Service/medimages4tests/pull/13


**Full Changelog**: https://github.com/Australian-Imaging-Service/medimages4tests/compare/v0.5.4...v0.5.5

What's Changed
* Fixed up caching, so that different header values are cached separately by tclose in https://github.com/Australian-Imaging-Service/medimages4tests/pull/12


**Full Changelog**: https://github.com/Australian-Imaging-Service/medimages4tests/compare/v0.5.3...v0.5.4

What's Changed
* Fix evolution of DICOM header PET raw data by tclose in https://github.com/Australian-Imaging-Service/medimages4tests/pull/11


**Full Changelog**: https://github.com/Australian-Imaging-Service/medimages4tests/compare/v0.5.2...v0.5.3

What's Changed
* added check for pydicom version before using enforce pydicom write by tclose in https://github.com/Australian-Imaging-Service/medimages4tests/pull/10


**Full Changelog**: https://github.com/Australian-Imaging-Service/medimages4tests/compare/v0.5.1...v0.5.2

What's Changed
* Fixes arg to dicom write so that `DICM` magic number is written by tclose in https://github.com/Australian-Imaging-Service/medimages4tests/pull/9


**Full Changelog**: https://github.com/Australian-Imaging-Service/medimages4tests/compare/v0.5.0...v0.5.1