OpenDKIM keys have been moved to the keys folder

This is to make it easier to integrate with Kubernetes to be able
to bind a `ConfigMap` to the said folder.

README.md

@@ -145,16 +145,13 @@ You'll need to create a  folder for every domain you want to send through Postfi
 
 ```
 mkdir -p /host/keys; cd /host/keys
-mkdir example.com; cd example.com
-opendkim-genkey -s mail -d example.com
-cd ..
-mkdir example.org; cd example.org
-opendkim-genkey -s mail -d example.org
+opendkim-genkey -b 2048 -h rsa-sha256 -r -v -s example.com -d example.com
+opendkim-genkey -b 2048 -h rsa-sha256 -r -v -s example.org -d example.org
 ```
 
 `opendkim-genkey` is usually in your favourite distribution provided by installing `opendkim-tools` or `opendkim-utils`.
 
-Add the created `mail.txt` files to your DNS record. Afterwards, just mount `/etc/opendkim/keys` into your image and DKIM 
+Add the created `<domain>.txt` files to your DNS records. Afterwards, just mount `/etc/opendkim/keys` into your image and DKIM 
 will be used automatically, e.g.:
 ```
 docker run --rm --name postfix -e "ALLOWED_SENDER_DOMAINS=example.com example.org" -v /host/keys:/etc/opendkim/keys -p 1587:587 boky/postfix

opendkim.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 if [ ! -d /etc/opendkim/keys ]; then
     sleep 9999999999999999999
-elif [ -z "$(find /etc/opendkim/keys -type d ! -name .)" ]; then
+elif [ -z "$(find /etc/opendkim/keys -type f ! -name .)" ]; then
     sleep 9999999999999999999
 else
     /usr/sbin/opendkim -D -f -x /etc/opendkim/opendkim.conf

run.sh

@@ -201,7 +201,7 @@ if [ ! -z "$MASQUERADED_DOMAINS" ]; then
 fi
 
 DKIM_ENABLED=
-if [ -d /etc/opendkim/keys ] && [ ! -z "$(find /etc/opendkim/keys -type d ! -name .)" ]; then
+if [ -d /etc/opendkim/keys ] && [ ! -z "$(find /etc/opendkim/keys -type f ! -name .)" ]; then
 	DKIM_ENABLED=", ${emphasis}opendkim${reset}"
 	echo  -e "‣ $notice Configuring OpenDKIM."
 	mkdir -p /var/run/opendkim
@@ -227,7 +227,7 @@ if [ -d /etc/opendkim/keys ] && [ ! -z "$(find /etc/opendkim/keys -type d ! -nam
 	echo "" >> /etc/opendkim/TrustedHosts
 	if [ ! -z "$ALLOWED_SENDER_DOMAINS" ]; then
 		for i in $ALLOWED_SENDER_DOMAINS; do
-			private_key=/etc/opendkim/keys/$i/mail.private
+			private_key=/etc/opendkim/keys/$i.private
 			if [ -f $private_key ]; then
 				echo -e "        ...for domain ${emphasis}$i${reset}"
 				echo "*.$i" >> /etc/opendkim/TrustedHosts