Added more documentation

[Lachee]

Improved the documentation some more. I removed the secret field in the JoinRequest (since it does not send any) and added some additional notes. Also included the structures for the responses.

[msciotti]

Thank you for these copious notes! Originally, the "hard mode" documentation was just intended for developers that already had RPC access, so it just had some basic info about RPC commands. While most devs will grab the SDK and be on their way, there's obviously a desire for native implementations like yours. This is very much appreciated for others going down the same path.

[sultan32]

static void UpdatePresence()
{
DiscordRichPresence discordPresence;
memset(&discordPresence, 0, sizeof(discordPresence));
discordPresence.state = "Playing Solo";
discordPresence.details = "Competitive";
discordPresence.startTimestamp = 1507665886;
discordPresence.endTimestamp = 1507665886;
discordPresence.largeImageText = "Numbani";
discordPresence.smallImageText = "Rogue - Level 100";
discordPresence.partyId = "ae488379-351d-4a4f-ad32-2b9b01c91657";
discordPresence.partySize = 1;
discordPresence.partyMax = 5;
discordPresence.joinSecret = "MTI4NzM0OjFpMmhuZToxMjMxMjM= ";
Discord_UpdatePresence(&discordPresence);
}