Eliminate need for apt-ftparchive

[mmstick]

Recently, the tool has gained support for generating the Contents archives in parallel. Similar logic can also be used for generating the Packages archives, which is currently handled by apt-ftparchive. The issue is that apt-ftparchive does not process Debian archives in parallel, so it can take a bit of extra time to process all the archives one by one.

• [x] Generate Packages for each architecture
• [x] Generate Release for each architecture
• [ ] Generate Release for a suite
• [ ] Generate Sources