Further isolate the output stuff...

...and change status reporting to standard error, since we're going
to use standard output for export.
Strip out more git machinery.  This version still makes graphs.
All git dependencies removed, and it can still make graphs.
More disentanglement from git pieces.
Now generating blobs.
More code elimination.
Now we dump the beginnings of fast-export commit headers.

This revision also removes the log-filtering feature.  While that made
sense in the original use case of this tool, it doesn't when the new
use case is to make it a pure exporter for programs like reposurgeon
and git-cvsimport.
Now generating correct commit headers.
Refactor.  Tags and fileops aren't dumped yet.
Refactoring step.
Now we emit tags.
Remove dead code.  Everything seems to be working except fileops.
Put a manual page and some metadata files in place.
Appropriately trim and translate the output filenames for export.
Generate M ops.
Another step tords full fileops.
We need a status field for generaying fileops.
Refactor.
Remove dead code.
Simplify computation of fileops.