Added UpdateButtons

[Almighty-Shogun]

This pull request will allow users to update and remove their buttons without having to restart the program.

You can use this code in the following way:

Updating all the buttons

When a user wants to update all their buttons from the current Rich Presence they can do the following:

client.UpdateButtons(new Button[]
{
    new() { Label = "ButtonLabel 1", Url = "https://domain.com" }, // Button 1
    new() { Label = "ButtonLabel 2", Url = "https://domain.com" } // Button 2
});

Updating a single button

When a user wants to update a single button from the current Rich Presence they can do the following:

Example: You have 2 buttons. The first one is a link to your website and the second one is a link to your Discord server. You want to update the second one with an up-to-date invite link you can do the following code:

client.UpdateButtons(new Button[]
{
    new() { Label = "Join our Discord", Url = "https://discord.com/invite/xxx" }
}, 1);

Removing buttons

When a user want to remove their buttons from the current Rich Presence they can do the following:

client.UpdateButtons();

If there are any follow up questions or things I might have missed let me know and I will look into it asap!

[Almighty-Shogun]

I forgot to mention that there was also an issue for this #147

[Lachee]

Overall good contribution. Only request minor change to the UpdateButton(Button[], int) call

[Lachee]

A better way to implement this function is to:

• Make it only take a single Button instead of an array
• Turn buttonId into index instead which starts from 0.
• Rename it to UpdateButton or SetButton

[Almighty-Shogun]

I'll look into the code later today for the minor changes you have requested

[Almighty-Shogun]

I implemented your request. I added that the index in the SetButton method is 0 by default. Users can now use this method by the following way:

// Using button as an variable
var newButton = new Button()
{
	Label = "Updated btn",
	Url = "https://github.com/Lachee/discord-rpc-csharp"
};

client.SetButton(newButton);

// Updating it without an variable
client.SetButton(new Button()
{
	Label = "Updated btn",
	Url = "https://github.com/Lachee/discord-rpc-csharp"
});