Allow @deprecated tag without version

Sometimes I don't have a version number in which something stopped being allowed, or don't remember at what point in time something became deprecated. It would be nice to be able to just have a flat out "no, don't use this because I said so, but it still exists for a weird archaic legacy purpose."

Currently I have to do something like:

`@deprecated {0.0} Don't use this, because I said so.`

Would be nicer to just have:

`@deprecated Don't use this, because I said so.`

Locate the parser or documentation handling for the @deprecated tag and compare how it processes the current versioned form. Confirm that a versionless tag is accepted while the existing form continues to work, and verify the resulting generated documentation reflects the supplied message.

Written by the indexing model from the issue text.