Removes rooms, replaced with cv_advertise and "Advertise" on the host menu.

According to the new API, SRB2APPLICATION is sent instead of MODID. A contact
field was added, but there is no means of accessing it or setting it.

As a slight change, the server list will be populated even on an outdated
version of the game. (The new API was designed with this in mind.) The update
alert is still presented first of course.

SetCurrentDirectory to where the exe lives

See merge request KartKrew/Kart-Public!219

Cause more issues than fixes. Still around for Linux.

Flush random map pool after all but 3 are played

See merge request !216

Caret color codes in server name

See merge request KartKrew/Kart-Public!218

Discord Rich Presence

See merge request !207

A and B are v2 terminology

(cherry picked from commit 679bfa21edec6b652def93082da5586e6c755678)

(cherry picked from commit 1f38db46298181d117432e12e88b326a92b4b785)

Attach initial join discord info to servercfg, so that we don't have a pause from needing to also send XD_DISCORD

XD_DISCORD is now reserved for when the options are changed mid-game

- Call DRPC_Init at the end of D_SRB2Main instead of in the middle
- Call Discord_RunCallbacks in D_SRB2Loop instead of G_Ticker
- Fix errorcount nums in I_Error, an old leftover from when Discord_Shutdown was not handled by I_AddExitFunction

Expose demo.playback to Lua

See merge request !217

Check ~/.srb2kart for srb2.srb

See merge request !215