Fix QPDFObjGen constructor implementation
Allow numeric range to be omitted qpdf --pages

Detect a missing page range and assume 1-z.
Add --show-npages option to qpdf
Adjust to-do list
Ignore broken DecodeParms for stream with no filters
Update for 4.2.0
Replace - with -- in documentation

This is a cosmetic change since both are accepted.
Update spelling checker word list
Prepare 4.2.0 release