emit full jsdoc for function types

[evmar]

Rather than emitting a type per parameter, emit a jsdoc
before the function declaration. This allows us to mark optional
arguments properly with the = suffix. Note the changed "optional.ts"
test; it now verifies that Closure accepts a missing argument when
that argument was missing before.

Fixes #43.

[rkirov]

looks like we lost the comment? But it appears in sickle/arrow_fn.ts, so I am very confused.

[rkirov]

Should we file a bug at https://github.com/google/closure-compiler/issues for function f(/** number= */) not working? Sounds like a bug to me.

[evmar]

function f(/** number= */) is expected to not work. Something about how = is not part of the type but actually part of the @param declaration. E.g. I think you can't declare a variable with a type that includes = in it.

[evmar]

Note that the weird output with the duplicated comment is due to
microsoft/TypeScript#6982

[evmar]

Reassigning to Martin because Rado is out today.

[evmar]

Travis is failing due to the compile timing out. :~( I guess I gotta refactor things to run the compilations separately. The compile succeeds locally though it takes a while.

[evmar]

With the timeout "fix" in place, this is now ready for review.

[rkirov]

I don't see how you fixed the timeout issue. But LGTM, since it looks fixed.

[rkirov]

I thought T= is sugar for T | undefined, but really it is marker for the function type. The more your know ...