Accumulate hits and miss costs instead of overwriting

[brk]

Currently, if a memory location is touched more than once, only the last touch is shown. It'd be nice to show all touches as the accumulate.

This may require another preprocessing pass to determine the maximum cost for any memory location; I haven't thought about it in great detail.

This would also tie in to simulating, and possibly showing, multiple levels of cache, in order to determine cost at a more fine-grained level.

[brk]

To clarify, there are several different subproblems here: method used to show multiple memory touches, and method used to show accumulated costs from multiple memory touches.

Showing multiple touches in an intuitive way will probably be the most problematic. Showing accumulated costs will I think be only slightly fiddly to implement, but is conceptually pretty simple.