New: DepotDownloader - downloader for Steam depots (i.e. games)

Hi,

I am pleased to offer this port as a solution for obtaining games
purchased on Steam without needing to boot into another OS. It was
discovered by anthk_ on the Freenode channel #openbsd-gaming and I
turned it into a port with a few quality-of-life enhancements in the
wrapper script.

The port downloads the CIL assemblies and installs a wrapper script.
Building would require msbuild which don't have (yet).

The wrapper script adds 2 modifications to make this more usable (until
they may be included into upstream):

1. add '-appname <name>' to download game by name instead of (numeric)
AppId
2. install to ~/games/steamdepots/<AppName> unless `-dir` is specified
- this prevents installing in $PWD by default

I've tested it with a few of my games (CometStriker, Salt and
Sanctuary, Cryptark, One Finger Death Punch) without problems. Note
that the appname needs to be in quotes/double-quotes; it may also work
with whitespace escaped. The assembly seems to assume "linux" as OS;
therefore if trying to download a game that is only distributed for
Windows, you need to add '-os windows'.

More info in the README of the repo [1], including how to download
Steam Workshop items/mods (not tested by me).

Of note, this works with the 2FA "SteamGuard" via email code. I don't
use the 2FA via the Steam mobile app and don't know if that also works.
Testing by someone who uses the Steam mobile app as the second factor
would be appreciated.

ok?

[1] https://github.com/SteamRE/DepotDownloader