Many legacy Awesome APIs such as `client:tags()`, `root.buttons()`,
`client:keys()`, `drawin:geometry()`, etc used functions for both the getter
and setter. This contrast with just about everything else that came after
it and is an artifact of an earlier time before we had "good" Lua object
support.
Because both consistency and backward compatibility are important, this
table wrapper allows to support both the legacy method based accessors
and key/value based accessors.
It isn't part of the public API, has a sledgehammer function prototype
and is intended for internal use only.
It's ugly, but backward compatibility is more important than anything
else.