Implement SUMMARY display for `top`

[Krysztal112233]

Currently our implementation output:

TODO

But the GNU's implementation:

top - 15:51:38 up 9 min,  1 user,  load average: 1.45, 1.09, 0.61
Tasks: 496 total,   1 running, 495 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.5 us,  1.7 sy,  0.0 ni, 94.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st 
MiB Mem :  31506.4 total,  20616.9 free,   5700.0 used,   5692.4 buff/cache     
MiB Swap:      0.0 total,      0.0 free,      0.0 used.  25806.5 avail Mem 

[Bluemangoo]

Hi, I'd like to work on this.

I found another crate systemstat, which partially overlaps with sysinfo, but provides something more like uptime and cpu time. Can we use it?

[cakebaker]

@Bluemangoo sure, go ahead :) It might make sense to split it into multiple PRs, similar to the documentation in the manpage.

There is also someone working on a TUI in #292, but I think this issue can be addressed independently.

[r3yc0n1c]

yes, I was working on this... didn't get much time lately... if you plan to use the multi-threaded background to refresh just like Krysztal112233 suggested in the PR, please refer to this discussion: #292 (comment) and It would be great if you could implement it in a way that allows me to call and render these from the tui mod.