* Accept grid patches and save them to hdf5
* possible ways of output:
  - one proc writes all to one file
  - each proc writes to own file
  - specify list of proc that would write to one file

* export structs that will have all required data for GDF

  1. create metadata struct
  2. pass it to lib, lib creates file, writes metadata, creates all groups, see piernik
  3. loop over grid patches passing them to lib
  4. lib happily writes the data
  5. closes file and cashes the check