Add PRAWErrors class for a better structure hierarchy.
Add PRAWErrors class for a better structure hierarchy.

Also add NotFound error that will encompass all 404/Not Found errors.

leviroth/praw,gschizas/praw,13steinj/praw,13steinj/praw,leviroth/praw,nmtake/praw,praw-dev/praw,praw-dev/praw,darthkedrik/praw,gschizas/praw,nmtake/praw,darthkedrik/praw,RGood/praw,RGood/praw