Additional tags needed in standard schema

[VisLab]

Propose adding the following tags to next release of standard schema (motivated by using HED tags in participants.tsv in BIDS):

• Add year as a unit under timeUnits unit class (ages are often given in year).
• Add Date under Informational-property with value class dateTimeClass.
• Modify the description of the of the dateTimeClass so that it conforms with the current BIDS specification found in common-principles:

  Date time information MUST be expressed in the following format YYYY-MM-DDThh:mm:ss[.000000][Z] (year, month, day, hour (24h), minute, second, optional fractional seconds, and optional UTC time indicator.

• Add Other-sex under Sex to capture BIDS option Other or O for the sex column in the participants.tsv file.
• Add Species under Metadata to capture new BIDS column species in participants.tsv file.
• Add DOI under Metadata to capture BIDS use of DOI in dataset_description.json and other places.

[VisLab]

HED already had Creation-date, so added Modified-date.

Added Other-sex under Sex to accommodate BIDS specification.

Used BIDS requirements and specification for species.

In PR #140.

[VisLab]

Added in PR#140