use NSFileManager.defaultManager()
replace source file lists in dependency URLs with attributes

A dependency specified as "git://.... <dir/file1.swift> <dir/file2.swift>" should be replaced with "git://.... @source:dir" from now on.

Having the @source attribute is a direct analogy to the "source" directory field in swiftmodule.json.
manage swm's dependencies via bower
add support for building the current package

The current package is built if a "source" directory field is specified in its swiftmodule.json. The .modules/ directory (containing all built dependencies) is used as the search path for import statements in the package.