dnscrypt-proxy: Add custom resolver config support

dnscrypt-proxy: Add custom resolver config support

This commit modifies the dnscrypt-proxy plugin's `dnscrypt-proxy.init`
script to allow specifying a custom dnscrypt resolver. Prior to this
commit users of the dnscrypt-proxy plugin are only able to choose from
a dnscrypt resolver that is present in the packaged `ResolversList` CSV
file.

To specify a custom resolver three new configuration parameters are
required[0]: `ProviderName`, `ProviderKey` and `ResolverAddress`.

The `dnscrypt-proxy.init` script now maps `providername`, `providerkey`,
and `resolveraddress` values (if present) from a `dnscrypt-proxy.config`
file into the generated DNSCrypt configuration file.

`PKG_RELEASE` is increased from 1 to 2 to reflect the new functionality.

[0]: https://github.com/jedisct1/dnscrypt-proxy/blob/9eee47477031ad0ffef94160d7370d4dec6f2c3a/dnscrypt-proxy.conf#L28:L32

Signed-off-by: Daniel McCarney <daniel@binaryparadox.net>