Add a new RIP utility library

Currently, this has RIP.supported which returns true if RIP is
supported by the client, and rip.loadicons(archive) which sends
all the icons (and .RIP files) in the specified archive (either
an Arcive object or a filename) to the remote if they don't
already have them.

If you have a RIP enabled door, a small JS script as a pre-run
command like this:

require("rip.js", "RIP");
rip.loadicons('/sbbs/xtrl/lord/lordicns.zip');

Will automatically send all the icon files in the arcive to the
user if the user doesn't already have them.  For SyncTERM as of
this commit, they will be placed in the cache directory for that
BBS (and only be available for that BBS).

On *nix, the cache dir is ~/.syncterm/cache/<bbsname>
On Win32 it's something like:
C:\Users\User\AppData\Local\Microsoft\Windows\INetCache\SyncTERM\cache\<bbsname>

No ideal what it is on macOS.