OpenSystemsDevelopment / qpdf

Also, make obj_cache private and rename to table.

Move methods responsible for loading or keeping track of objects to
QPDF_objects.cc.

Also, tidy pipeline constructors and make subclasses final where possible.

Add new commands --remove-metadata and --remove-info

Tokens longer than the target cannot be a match and therefore there is no
need to read to the end of token.

Return results rather than using reference parameters.

Fixes bug in #1272 where parameters were not reinitialized when calling
read_bad_entry from read_entry.

Currently, QPDFParser gives up attempting to parse an object if 5
near-consecutive bad tokens are encountered. Add a limit of a total of 15
bad tokens in a single object before giving up.

Also, delay adjustments for compressed objects until needed by
linearization checks.

Optimistically read subsection headers without reading individual object
entries, assuming that they are 20 bytes long as per the PDF spec. If
problems are encountered, fall back to calling bad_subsections.

Replace QPDFXRefEntry with a std::variant of structs.

Temporarily disable 3 specific-bugs tests. Remove 'xref size mismatch'
test.

Split reconstruction into two passes - scanning of input for objects and
insertion of objects into the xref table. This allows insertion to take
place in the usual reverse order and removes the need for a separate
insert_reconstructed method.

Rename to Xref_table::process_section.
Process trailer processing subsection entries.

Calculate all subsections before reading subsection entries.

Duplicates some warnings for the time being.

Rename to Xref_table::subsection.
Return results instead of using out parameters.
Take on responsibility for throwing exception and calculation of offset of
first subsection entry.