[Python-3000] Set literal

[Charles Merriam]

> There are also « and », << and >> for those w/o UTF-8 support in their
> mail client. On my keyboard the characters are available under [alt gr]
> + y and x.

Not elegant.  It should look pretty.  Code should look the same in all
character encodings unless alternate codings for used for identifiers.

Seriously, people just want to code in Python without odd little nooks of lore.
Over 99.9% of programmers will not care about a minor performance hit
for no compile-time frozen sets.

Cheers,

Charles