Memstats Improvements

[1stub]

As I've been working on getting the decs processor running better I found my previous memstats output to be annoying to read and some computations were not correct. This is a rework of the formatting and cleanup of logic.

We now always compute nursery and rc old timings as well. There is still more work to be done here, but I believe this to be a good baseline.

e.g.

Performance:
    Measurement        Mean          σ         Min         Max        50%         95%          99%
     Collection   911.893us   358.652us   642.533us   4.86352ms       804us      1.57ms      2.49ms
        Nursery   47.5185us    26.805us    14.289us   173.833us        32us        86us       110us
         RC Old   17.1174us   12.2533us     0.241us   124.634us        10us        36us        52us
Statistics:
        Total Time        12.555s
        Time Collecting   17.3446%
        Total Collections 2.388K
        Total Pages       1.063K
        Max Live Heap     37.64KB
        Heap Size         8.7081MB
        Alloc Count       348.765M
        Alloc'd Memory    17.1287GB
        Survival Rate     0.154329%