organize the metadata from the sar leader file

[keewis]

part of #17

The SAR leader file contains a huge amount of metadata, with lots of sections that on their own are often bigger than the volume leader file. As such, I think it makes sense to have a separate organization issue.

These are the sections that need to be transformed:

• file descriptor (ignored, since it doesn't contain any new metadata)
• dataset summary (organize the metadata in the dataset summary record #30)
• map projection (organize the metadata in the map projection record #31)
• platform position (organize the metadata in the platform position record #32)
• attitude (organize the metadata in the attitude record #33)
• radiometric data (organize the metadata in the radiometric data record #34)
• data quality summary (organize the metadata in the data quality summary record #35)
• facility-related data, 1-4 (ignored for now, see investigate the contents of the auxiliary files #38)
• facility-related data, 5 (organize the metadata in the facility-related data records #36)

And finally, they need to be integrated into a single function:

• integrate the sar leader transformers #37