add make-single-file-spm (#1236)
add make-single-file-spm (#1236)

Motivation:

make-single-file-spm is a simple bash script that can turn a single file
into a SwiftPM project with multiple modules (all defined in a single
file with special markers such as `// MODULE: Foo`. This is mostly
useful for performance evaluation of Swift becuase in almost all cases,
you'll need multiple modules which is quite a bit of work to set up.

Modifications:

Add make-single-file-spm

Result:

More useful scripts in the NIO repo.
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio