Allow regular letters as operator names

[Lantua]

@total_swiftification

So why they don't want this feature if it can be done? Is this mythical complexity increase they afraid of?
[...]
Notice that I am not proposing to replace them.

I suggest you read the linked discussion thread.

Here's a response from Cris, from the discussion thread, which I believe still holds true.

@Chris_Lattner

The rationale is the same - the design of Swift really wants operators and identifiers to be partitioned into different namespaces. Violating that would make it impossible to parse a swift file without parsing all of its imports. This is a mistake that C made (you have to parse all the headers a file uses to reliably parse the file) that we don’t want to replicate in Swift.

-Chris