[enhancement] return_if

[ColinFay]

Wrapper around

if (this) return(x)

[ColinFay]

I think we could also go for things around return_if_is:

return_if_is(this, "numeric", that)

Which could also work for

stop_if_is(this, "numeric", message) 

Ideas :

• *_if_equal
• *_if_null
• *_if_length
• *_if_matches