[Feature request] Support system hosts file

[T1mL3arn]

A setting to read system hosts file. We have cloaking_rules settings and cloaking-rules.txt file. But its syntax is not the same as hosts syntax. Hosts file can already have a lot of rules (e.g. in heavily censored regions) so it seems logical and convenient to make it work with dnscrypt-proxy without any converting to cloaking syntax.

It could like that

ignore_system_hosts = false

or

path_to_system_hosts = 'a/b/c/hosts'