Add support for returning aliases of a given character

[eugenesvk]

println!("\u{7f} is called {:?}", unicode_names2::name('\u{7f}')) results in None instead of Delete, same for other control chars

[progval]

Relevant line from UnicodeData.txt:

007F;<control>;Cc;0;BN;;;;;N;DELETE;;;;

According to https://www.unicode.org/Public/3.1-Update/UnicodeData-3.1.0.html , <control> while DELETE is the "old name as published in Unicode 1.0". So the current behavior is correct, though I don't understand it. It's also documented here: https://docs.rs/unicode_names2/latest/unicode_names2/fn.name.html

However, this character does have two aliases: DELETE and DEL. I would accept a PR adding support for returning a list of aliases of a given character, gated behind a feature flag.

[eugenesvk]

I also don't understand how the current behavior is correct when you have a name (either an old one or the "aliased" one). What's the point of NOT using it and complicating the use by pushing this distinction onto the unsuspecting users?

FYI https://github.com/JuanPotato/charname returns the names for control chars
Python is weird

x1 = lookup("BACKSPACE") # works, can find a control char by name
print(x1)
# x1nm = unicodedata.name(x1) # fails to find a name by code

[progval]

🤷 you have to ask the Unicode Consortium