[latexrefman] Small modification (or extension) to 28 Command line

[Karl Berry]

    a more suitable title would be:
    28 Command line interface

Agreed, changed.

    And I would add a small description of CLI implementing (I do not know
    if it is POSIX or GNU) 

FYI, long (two-dash) --options, among other ubiquitous command line
parsing features, are GNU, but we don't need to say that.

    next move the text that is in 28.1 here

Option syntax is about options, so it didn't seem right to move it to a
different node.
    
    Next to a note regarding the `=` sign that is mandatory for options
    that take a value and should not have spaces before or after it.

Either --foo=val or --foo val works (but not -foo= val). I added some
text about it.

Thanks,
Karl