[BUGFIX] Prevent corrupt writes to download archive (983)
Attempts to make writes to the download archive safer (https://github.com/jmbannon/ytdl-sub/issues/982).
`ytdl-sub` will now *copy* the download archive from the working directory to the output directory with a temp name, then perform a *move* to store it with its final expected name. This will drastically lower the window of time where the process could die mid-write and corrupt it on the next read.