The short name is limited to 1 char

Version 1.73.0

Documentation (https://www.boost.org/doc/libs/1_73_0/doc/html/boost/program_options/option_description.html#id-1_3_31_9_7_1_1_2_5-bb):

> The 'name' parameter is interpreted by the following rules:
> if there's no "," character in 'name', it specifies long name
> otherwise, the part before "," specifies long name and the part after -- short name.

Code, options_descriptions.cpp, line 205:
```
if (last_name.length() == 1) {
m_short_name = '-' + last_name;
m_long_names.pop_back();
```

This limitation is not mentioned in the docs.
I would prefer that short names of several characters are allowed, but otherwise the limitations should be at least mentioned.
Side note: the possibility of having several long names separated by colons is not mentioned there, either.