Expanded help text for "Loadable Modules".
Expanded help text for internal code prefix/suffixes and some other edits.
Internal-code prefixes are now automaitcally removed from imported file areas,
just like was already done for message areas, by the prep_code() function.
Imported internal-code suffixes are converted to upper case.
Updated indentation and brace style.
Replaced special unprintable help text chars with ASCII equivalents (` and ~).