Log Message:
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.