Fix broken link to Strange Loop talk
"lfs"'s rock is actually called "luafilesystem"
Add basic garbage collection for forgotten files' chunks.

This does more disk IO than necessary -- it actually reads all the
content off disk, rather than just reading the metadata and skipping
the actual content. This can be fixed later, but would require the
Jumprope library to allow more control over content walking.
Update README.md to note that GC is now implemented.
Add 0.1-0 rockspec
add lrandom to rockspec