Clean up files after processing

[unix1]

This is the implementation of feature described in Packet-Clearing-House/DNSAuth#15. It adds a couple of configuration options to dnsauth.toml and implements associated logic to handle file cleanup after processing has been completed.

There are also a couple of code cleanup changes (in separate commits):

• renamed aggreagate to aggregate
• logged path of config file parsed at startup
• renamed variable filepath to avoid conflict with the package by the same name

[mrjones-plip]

@unix1 - Code looks good! Can you add some entries into the README.md about the new config options (move vs delete vs none)?

[unix1]

@Ths2-9Y-LqJt6 yep, done in 054ba4d.