[Swift] Tuple destructuring, function call with lambda argument

[dan-zheng]

I added Swift support for tuple destructuring: addresses issue #833.
I also fixed function calls with lambdas as the first argument.

Before:

When tuple destructuring occurs, let/var are incorrectly parsed as function names instead of keywords.

After:

Tuple destructuring is parsed as expected.

[johnfairh]

Nice - could maybe support backticks around the identifier - currently gives parse errors:

(and oops, now I notice the non-destructuring form with backticks gives the wrong syntax type...)

In case you haven't seen it there's a spec/visual/samples/swift file where your examples could go.

[dan-zheng]

Good catches!
I added a rule to handle backticks around identifiers in tuple destructuring.
I also fixed the syntax type of the non-destructuring form with backticks.

I added examples to the spec/visual/samples/swift file, as you suggested.

[gfx]

Cool. Thanks for your contributions.