Feature/mw/rtq percentage used

[lordnull]

Addresses #433 .

[bowrocker]

Testing

[x] manual verification of code
[x] eunit: https://gist.github.com/bowrocker/d86880522fb5d8526680
[ ] EQC N/A
[x] riak_test https://gist.github.com/bowrocker/2e661d505393aa8b8a8d
[ ] Dialyzer
[ ] XRef
[ ] Coverage reports

Documentation

[x] doc in code
[ ] internal docs (design docs)
[ ] external docs (docs.basho.com)
[ ] man pages

Output

New stats with percentage at the top looks nice:

07:41:53.498 [info] queue status: [{percent_bytes_used,0.035},
07:41:53.498 [info] {bytes,36735},
07:41:53.498 [info] {max_bytes,104857600},
07:41:53.499 [info] {consumers,[{"B",
07:41:53.499 [info] [{pending,85},{unacked,0},{drops,0},{errs,0}]}]},
07:41:53.499 [info] {overload_drops,0}]

👍