how to handle metadata

[Lyuba Zehl]

This issue should discuss how metadata should be handled in neuroscience-data-structure (NDS).
Within this issue we should discuss :

• metadata schemas, e.g.:
  • https://github.com/G-Node/odml-terminologies
  • http://neuroshapes.org/
• what is required, what is optional, what can be additionally provided?

How this is handled in BIDS:

• preferred formats: TSV and JSON
• schemas: are defined in the specs and somewhere in the GitHub repo (I think)
  Metadata properties can be required or optional. Not sure if you can provide additional properties.

The matter of preferred metadata file formats is discussed in #2