feature: unhex of in-line HEX

Support in-context unhex of outfiles / potfiles / etc.

For example, this input:
```
96a1bbb41c713dce96b49dd13b6f6d07:$HEX[636f6c6f6e3a636f6c6f6e]
```
... should produce this output:
```
96a1bbb41c713dce96b49dd13b6f6d07:colon:colon
```