Survey users/data scientists on plain text representations of superscript and subscript

[ahamelers]

From #2472. If we allow italics, superscript, and subscript in our titles for display on Dryad, we will need to remove them for APIs (Dryad, DataCite, etc.)

In surveying other APIs, italics are generally removed without comment, but superscript and subscript are indicated in a number of ways. There does not seem to be a general consensus about how to represent these in plain text.

Some mathematicians at least should be able to read something like ^(3)He for ³He and C0_(2) for C0₂

Before implementing this in titles, we should reach out to the Dryad community, particularly anyone who uses the API, to decide on a method.

[ryscher]

This is a more specific instance of #2621

[ahamelers]

After checking standards again it would be best not to allow html sub and sup entitites, but to allow unicode mathematical characters which include superscript and subscript