v0.4.0

• The ubi CLI tool now takes an optional --extract-all argument. If this is passed, it will only look for archive files and it will extract the entire contents of an archive it finds. There is also a new corresponding UbiBuilder::extract_all method. Requested by @Entze (Lukas Grassauer). GH #68.
• The UbiBuilder::install_dir method now takes AsRef<Path> instead of PathBuf, which should make it more convenient to use.
• Previously, ubi would create the install directory very early in its process, well before it had something to install. This meant that if it failed to find an asset, couldn't download the asset, or other errors happened, it would leave this directory behind. Now it creates this directory immediately before writing the executable it found to disk.