OpenSystemsDevelopment / qpdf

Reflect that the ls_number case only handles the digits after an 'e'.

Also, change state to ls_number for all 'ready' numbers.

Also, allow 'E' as alternative to 'e'.

Also. remove '.' as  starting char in lsTop.

Code tidy : replace 0 with nullptr or true

When the schema wants a variable-length array, allow a single item as
well as allowing an array.

Call the parent container's item method before calling the child
item's start method so we can easily know the current nesting level
when nested items are added.