Cleanup the repository

[lunaisnotaboy]

This cleans up the repository's code. It is just minor things like formatting and layout, nothing else.

An .editorconfig was added for standardization of settings between different editors, and an improved .gitignore was also added. The .idea directory is now ignored due to it often being changed by users.

This will also allow code to be read more easily on smaller displays, such as my laptop.

Code is transformed from this:

public static StringBuilder AppendHtml(this StringBuilder builder, string tag, string? attributes, Action contents)
{
    builder.Append($"<{tag}");
    if (attributes != null)
    {
        builder.Append(' ');
        builder.Append(attributes);
    }
    builder.Append('>');

    contents();

    builder.Append($"</{tag}>");
    return builder;
}

To this:

public static StringBuilder AppendHtml(
    this StringBuilder builder,
    string tag,
    string? attributes,
    Action contents
) {
    builder.Append($"<{tag}");

    if (attributes != null) {
        builder.Append(' ');
        builder.Append(attributes);
    }

    builder.Append('>');

    contents();

    builder.Append($"</{tag}>");

    return builder;
}