This allows plugins to update and cache data files from a remote source.
Here are the steps that occur when the API initiates an update check:
1.) It checks to see if the local files are greater than the cached
files. If the local version is newer (for whatever reason), it
replaces the cached version(s) with the local version.
2.) A packages.json file is downloaded from the specified URL. That
packages.json file contains a version number and a list of files to
be updated.
3.) If the downloaded package version is greater than the cached
version, executes step 4-5 on each file.
4.) Checks the version for the file to update in packages.json, and if
the version is greater than the cached version, proceeds to step 5,
otherwise repeat step 4-5 for other files.
5.) Calls the callback given to the update function (if any) with the
file information (file name, buffer, etc), and if the callback
returns true, allows the cached file to be updated and replaced,
otherwise goes back to step 4-6 for the rest of the files.
NOTE: Files are never modified directly. All file saving/modification
is performed in a temporary directory, and then files are moved to their
destination. This should eliminate any possibility of file corruption
(or at least dramatically reduce the possibility).
