Verona spec: Add `.` to $OPT

[Iris Clark]

Hi.

In response to a request to add `.` as a valid character in $OPT, I've modified the specification as follows:

<   - <a name="descSTR"/> $OPT, matching `([-a-zA-Z0-9]+)` --- Additional
---
>   - <a name="descSTR"/> $OPT, matching `([-a-zA-Z0-9\.]+)` --- Additional

Please let me know if there are any concerns.

Thanks,
iris