New formats for bytes and bits with standards-compliant abbreviations

[wylieconlon]

Instead of changing the behavior of the "b" formatter I have added four new formatters. #15

• Does not change the b bytes formatter, which uses base 1024, even though it could be considered non-standard. The non-standard formatting is used by Elasticsearch, where 1kb=1024 bytes
• Introduces the bd bytes decimal formatter for base-1000 bytes (kB, MB, GB)
• Introduces the bb bytes binary formatter which displays kibi/mebi/gibi bytes per the SI standards (KiB, MiB, GiB). Despite being a standard, it is less popular and might not be the appropriate default.
• Introduces the bitb bits binary formatter for base-1024 bits (kibit, Mibit, Gibit)
• Introduces the bitd bits decimal formatter for base-1000 bits (kbit, Mbit, Gbit)

elastic/kibana#7543

[timroes]

Looked at code and tests and LGTM. I think there are some optimizations we could make around the code, but I would not consider those part of this PR, and also questionable if we still want to do, if we want to switch to Intl anyway.

[timroes]

LGTM. @spalger would you mind a second review?

[spalger]

LGTM