Add .as_wsgi/.as_view methods.
Don't make setup.py executable.
Allow rules to use generated output (first pass)
Combine TargetFile and Target objects, and introduce TargetDir
Calculate/use modification times for determining when to rerun builds.
Clean up rules.
This will assurably be 0.2, or at least, not 0.1
Restore ablity to "install" static files.

It might be desirable to be able to exclude files from final output,
so .build_all() isn't really a good solution.
Don't require output directory (although it's advised)
In .as_wsgi, handle getting no response from the view.
Change path normalization to convert paths to native paths.
Consult filesystem for mtime instead of caching it.
Don't try symlinks to directories as directories we can recurse into.
Fix comment sections names.
Rework build kwargs handling, add verbose.
Allow post-rules to run again.
Warn if it looks like there is a dependency cycle while generating targets.
Add manifest to describe which paths to export.
Don't try to set mtime on TargetSrc objects, since they get it from the file.
Fix native_to_url_path() utility (.install() depends on it)