This updates the module documentation to be more synced with other
modules. Also, this module on the first glance doesn't do what most
people might think. Because when condition evaluates to false, internal
cache remains with the same value, and a local variable is created with
the value provided in the last argument.
- Command arguments described separately and their placeholders renamed
to more intuitive names.
- More examples added, starting with a very basic syntax usage to more
complex ones, each described in more details.
- Each example has include() added to be more clear that this is a
module command.
Revise docs for all "Scripting Commands", except four find_XXX
that use a macro suite of their own.
* Take full advantage of the improved syntax highlighting.
* Make consequential use of <..> placeholders.
* Clarify things here and there in the text.
Specific improvements to some command docs:
* "math": Correct description of novel hexadecimal capability.
* "if", "foreach", "while": Provide link to "endif" etc
* "foreach", "while": Mention "break" and "continue".
* "foreach": Simplify explanation of ``RANGE`` and ``IN`` signatures;
advise against negative arguments or reverse ranges (compare issue #18461)
* "endif", "endfunction" etc: Explain that the argument is optional and
maintained for compatibility only
