Added extra subreddit name compatibilty.
Added extra subreddit name compatibilty.

This allows `GetSubreddit` and `GetSubredditAsync` to handle subreddits with the format "/r/Subreddit/", with the slash at the end. This previously gave a not-very-informative 404 error.
theonlylawislove/RedditSharp,tomnolan95/RedditSharp,chuggafan/RedditSharp-1,RobThree/RedditSharp,nyanpasudo/RedditSharp,pimanac/RedditSharp,CrustyJew/RedditSharp,angelotodaro/RedditSharp,Jinivus/RedditSharp,justcool393/RedditSharp-1,SirCmpwn/RedditSharp