Deprecated SPDX licenses are marked as unknown

The documentation for the SPDX License List states:
> "When a license identifier is "deprecated" on the SPDX License List, it effectively means that there is an updated license identifier and the deprecated license identifier, while remaining valid, should no longer be used. "

"wxWindows" is one of the deprecated license but it's marked as an unknown license key when trying to validate it with the code below.
```
expression = get_spdx_licensing().parse("wxWindows")
print(get_spdx_licensing().validate(expression))
```
Other deprecated identifiers containing an exception like "GPL-2.0-with-autoconf-exception" are also marked as unknown. I am not sure if this has to do with #82 but I think these should also be accepted.