This is a massive rewrite of the help text and cli.rst section of the
manual. All command-line flags now have their own help and are
specifically index. qpdf --help is completely redone.
Move most of the methods called from qpdf.cc after argument parsing
into QPDFJob. In this increment, enough QPDFJob API has been added to
handle the branch of QPDFJob::run() that creates output with an
appropriate division between qpdf.cc and QPDFJob.
There are temporary bits of code to enable everything to compile and
pass the test suite, including some duplication and hard-coded values.
