Add filtering to Gen

[nai888]

Is your feature request related to a problem? Please describe.
There is currently no way to filter Gen's results. This should be added via filtering.

Describe the solution you'd like
Add the ability to use ^ carets to filter certain results. For example, if V is a subpattern a/i/u, the pattern [VV]^aa^ii^uu would produce the results ai au ia iu ua ui but never any of aa ii uu.

Additional context
You can find the instructions for using this feature within Awkwords in its help file.