Typings and Native fs.copyFile() support

Along with a host of new copy methods:
copyFileAtomic - same as the promisified version of fs.copyFile, but replaces the destination atomically.
createFileCopy/ensureFileCopy - ensures folder structure before making the copy, dynamically creating directories where needed.
createFileCopyAtomic/ensureFileCopyAtomic - Same as createFileCopy/ensureFileCopy, but replaces the destination atomically.