Aliases are stored as plaintext files in the $NVM_DIR/alias dir.
They may store either an explicit version (v0.3.6) or an implied version
("latest"). The latter is a "moving target", and thus possibly
dangerous, but can be useful, too.
Adds a cache of all versions available on nodejs.org using simple empty files as placeholders. When a new version is installed, it will replace the placeholder with a directory.
This makes it easier for users to see what versions are available for install, and what the latest and stable versions are.
Isaac Wolkerstorfer