Let users spend points on single-use save points

[benslv]

• users can buy save points with a certain number of points (e.g. 500)
• can used on a per-sever basis (no cross-server spending)
• using a save creates a point at whatever the current count is, rather than defining it as a command argument
• if a count is wrong, the bot looks for the highest available save point that is lower than the current count, and resets the count back to it.
• save point is then deleted

[benslv]

changed third point to let users specify the count to add the save point at, but it has to be lower than the current count (i.e. can't set a save point at 100 if the current count is only 50)