fix debug max lifetime
fix percentage printout
make sure file is closed if any exception (e.g. LifetimeExceeded) happens
add lengthy_download module, which handles partial downloads and changing content
make lengthy download return ETag as well as filename
use XDG cache directory, not /tmp, for caching partial downloads; closes #2
add nose2 configuration: capture logs and output from failed tests
ignore more editor backups and build products
gut download and make it use lengthy_download instead, which is nicer and more tested