orcus: Update to 0.18.1

Changelog:
0.18.1
sax parser
* added support for optionally skipping multiple BOM's in the beginning of
  XML stream. This affects all XML-based file format filters such as
  xls-xml (aka Excel 2003 XML).
xml-map
* fixed a bug where XML documents consisting of simple single-column
  records were not properly converted to sheet data.
xls-xml
* fixed a bug where the filter would always pass border color even when
  it was not set.
buildsystem
* added new configure switches --without-benchmark and --without-doc-example
  to optinally skip building of these two directories.

0.18.0
general
* fixed the flat output mode to properly calculate the lengths of UTF-8
  encoded strings.
* replaced all uses of std::strtol() to parse_integer() to properly
  parse strings that are not necessarily null-terminated.
* added a new output format type 'debug-state' which dumps the internal
  state of the populated document model in detail. This can be useful
  during debugging.
* separated the import_shared_string interface implementation from the
  backend shared strings store per separation of responsibility.
* merged the foo_t and foo_active_t struct pair, such as font_t and
  font_active_t, in the styles store into a single type using std::optional.
* revised the documentation and public API and cleaned things up where
  necessary.
ods
* re-implemented the number format styles import to correctly keep
  track of element stacks and correctly perform structure checks to
  detect malformed documents.
  * added new interface to import named styles applied to columns.
  * added new interface to import attributes for asian and complex
    scripts for the folloiwng font attributes:
    * font name
    * font size
    * font style
    * font weight
  * re-designed the styles import interface to make it multi-level.
  * re-worked the import of the style:text-underline-width attribute
    to make its handling more in line with the specifications.
xls-xml
  * added support for importing wrap-text and shrink-to-fit cell format
    attributes.
  * added support for importing cell-hidden and locked attributes.
  * added support for importing direct and named cell formats applied
    to columns and rows.
xlsx
  * added support for importing wrap-text and shrink-to-fit cell format
    attributes.
  * added support for importing direct and named cell formats applied to
    columns and rows.
xml-map
  * added a new interface to pass the encoding information to the document
    model so that it can correctly decode non-UTF-8-encoded string values.

(ryoon)