bug#24603: [RFC 09/18] Implement special sigma casing rule

[Eli Zaretskii]

> From: Michal Nazarewicz <mina86@mina86.com>
> Date: Tue,  4 Oct 2016 03:10:32 +0200
> 
> In Greek, a sigma character has two lower case forms which depend on
> their position in the word.  Implement logic determining it.

Once again, can we store the needed conversions from
SpecialCasing.txt, instead of hard-coding them in C?

> +*** Greek small sigma is correctly handled when at the end of the word.
> +Strings such as ΌΣΟΣ are now correctly converted to Όσος when
> +capitalised to follow rules of Greek spelling.
   ^^^^^^^^^^^
US English spelling, please.

Also, I suggest to show the previous "capitalization" results as well,
and explain the difference, as the difference is subtle and may not be
clear to the reader.

Thanks.