Add rf_local_is_in function

[vpipkt]

To dos:

• tests currently failing. Some kind of type error in encoding or something
• add function to docs
• add Python bindings
• update masking docs to use it.

[vpipkt]

I am building the docs locally just to make sure the fix of #310 doesn't break anything.

@metasim let me know if docs look good and resolve your questions. We can embed a very short example.

[vpipkt]

Local docs build was successful.

[vpipkt]

See #400 which triggers circle CI docs build so we can see the final docs.