Support for changing `saves` path at runtime

[collinsmith]

#122 added support for the saves cli argument, however it may be more appropriate for this to be variadic and support changing this at runtime. If saves were implemented as a cvar, I could leverage the existing cvar code which provides file path suggesters to autocomplete the saves path.

c20978b and 3e9b01b added home and saves commands which will either need to be deprecated and removed or modified to work with any change made by this issue (should I decide to support a command syntax like saves C:\path\to\saves) -- I think a cvar impl may be easier.