[Pas2js] Additional ZenFS demo

[Michael Van Canneyt]

Hi,

Some improvements/additions were made to the zenfs support in pas2js.

https://www.freepascal.org/~michael/pas2js-demos/zenfstree/

The ZenFS filesystem as used in the demo, uses browser local storage to
store files. They are not easily viewable since they can be encoded in the
local storage. The contents are also not easily retrievable since they are
stored using a kind of inode system, and mapping a name to an inode is not
trivial.

The demo shows how these 'virtual' files can actually be downloaded and saved 
to disk. It also showcases a small file-explorer-like component which can show the
contents of the ZenFS filesystem.

Enjoy,

Michael.