conditional expressions don't work in a formatted string

[shirleyquirk]

please try to break it! i'm sure there's edge cases I haven't found

curly brackets can also be used, backslash escaped, so that table/json 
constructors can be used: 
    
    
    import tables,strformat
    let (foo,bar) = (3,4)
    assert&"""{ toTable( \{"foo": foo, "bar": bar \} ) }""" == """{"foo": 3, 
"bar": 4}"""
    
    
    Run