Support for binary downloads

[rdmark]

One of the critical feature gaps that I see with this web proxy compared to other vintage web proxies is support for downloading binary files. Some examples:

GET: http://macintoshgarden.org/sites/macintoshgarden.org/files/games/Goofy_Golf_Deluxe.sit
Error: Unsupported Content-Type: application/x-stuffit;
    at Server.<anonymous> (/home/dmark/dev/68kproxy/index.js:110:23)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)

GET: http://macintoshgarden.org/sites/macintoshgarden.org/files/games/Myth_II_Update_1.3.bin
Error: Unsupported Content-Type: application/octet-stream;
    at Server.<anonymous> (/home/dmark/dev/68kproxy/index.js:110:23)
    at runMicrotasks (<anonymous>)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)

GET: http://www.nethack.org/download/3.2.2/nethack-322.tgz
Error: Unsupported Content-Type: application/x-gzip;
    at Server.<anonymous> (/home/dmark/dev/68kproxy/index.js:110:23)
    at processTicksAndRejections (internal/process/task_queues.js:97:5)