Add Patch Level and File Format Version

- the splash version should reflect the changes in the API
- the created hdf5 structure does not nessesarily correspond to the API
  version, therefor we add a format number reflecting the structure and
  meta data changes for external tools not using splash for e.g. reading
Add Patch Lvl Reading to CMake
Merge pull request #80 from ax3l/topic/versions

Add Patch Level and File Format Version Close #73