swift234

[docs] Sketch out a Modules Build Model doc.

This doc will contain the underlying build model for a multi-file Swift
framework or application module. This model will then be driven by
Xcode to build a target.

The biggest open questions are in how Swift and Objective-C will interact.

<rdar://problem/14579792> TLF: Swift 1.0 Modules

Swift SVN r9244