Added a more intuitive helper struct when printing ByteSize

[ChanTsune]

The Display trait currently implemented in ByteSize only supports decimal prefixes.
If we want to use a binary prefix, we need to use ByteSize::to_string_as.
I have added helper some struct and methods to use them to ByteSize to make these more intuitive with refer to std::path::Path.

use bytesize::ByteSize;

assert_eq!("100 B", format!("{}", ByteSize::b(100).binary_display()));
assert_eq!("1.8 TiB", format!("{}", ByteSize::tb(2).binary_display()));

assert_eq!("100 B", format!("{}", ByteSize::b(100).decimal_display()));
assert_eq!("2.0 TB", format!("{}", ByteSize::tb(2).decimal_display()));

If you like this PR, it would be my pleasure if you merge it!

[ChanTsune]

@robjtede I resolved conflict!

[robjtede]

We'll chat about this approach once #69 is merged

[robjtede]

I took inspiration from this and the cookie crate to come up with #76. I think it's more extensible to use a single type with an inner format selection vs distinct types with display impls.

Thank you for your contibution to the project 🎉 this has been a much needed feature request imo.