net block: improve throughput formatting

[ammgws]

(Mostly?) Resolves #240.

@GladOSkar Thanks for doing the legwork on this one!

This also uncovered a calculation error with use_bits, which is now fixed.

Comparing the new default format (max 3 digits, minimum unit K):

new format: '46.8M'	 with use_bits: '0.37Gb'
cur format: '   46M'	 with use_bits: '  368M'

new format: '6.81M'	 with use_bits: '54.5Mb'
cur format: '    6M'	 with use_bits: '   48M'

new format: '0.81M'	 with use_bits: '6.51Mb'
cur format: '  813k'	 with use_bits: '    0M'

new format: '13.6K'	 with use_bits: '0.11Mb'
cur format: '   13k'	 with use_bits: '  104k'

In my opinion this is now way better than before. The only caveat may be when using use_bits as in the first example above - perhaps we should display in megabits instead of gigabits for that case. However I will leave that for a future PR.

[GladOSkar]

Wow, i wrote that almost 2 years ago :D Not quite what i'd call beautiful code but it does the job

[ammgws]

If you're up for beautifying it then please go ahead!

[GladOSkar]

I played around with it for a while and it doesn't actually get a lot better so... meh ¯\_(ツ)_/¯

[GladOSkar]

I wonder if this could be adapted into the speedtest block as well, because the formatting of that one annoys me to the point that i always patch it before updating i3status-rs... But the values are obtained in a very different way there

[ammgws]

I created a new issue for that.

By the way do you have any other improvements you'd like to share? (or maybe put your forked repo online?)

[GladOSkar]

No, it's really just a hardcoded removal of everything after the decimal points in the speedtest block