Feature request: auto-generated module.modulemap for working with swift (--swift-friendly)

Hi,

Nowadays (Version 7.3.1 (7D1014)) Xcode forces you to modularly (i.e. `module.modulemap`) import the objc header files.

It would be nice if the buildscript would auto-generate the proper modulemap, inside `dist/include` and the separate frameworks.

So for instance:

```
module j2objc {
// import IOSArray IOSClass IOSObjectArray IOSPrimitiveArray IOSReflection J2ObjC_common J2ObjC_header J2ObjC_source J2ObjC_types JavaObject JreEmulation JreRetainedWith NSCopying+JavaCloneable NSDataInputStream NSDataOutputStream NSDictionaryMap NSException+JavaThrowable NSNumber+JavaNumber NSObject+JavaObject NSString+JavaString jni etc.
umbrella "."
explicit module * { export * }
//or: header "JavaObject.h", header "IOSClass.h", header "IOSArray.h" etc.

framework module google {
umbrella header "google-umbrella.h"
export *
module * { export * }
}

explicit module android {
explicit module os {
umbrella "android/os"
explicit module * { export * }
}
}

// etc.
}
```