INI file section support

Hello!

I have added section support for ini files.

It's a common situation:

<pre>plugin.aes.serializer = yaml
plugin.aes.send_pubkey = 1
plugin.aes.client_private = client_key
plugin.aes.client_public = client_cert
plugin.aes.server_public = server_cert</pre>

With this patch it looks a bit better:

<pre>[plugin.aes]
serializer = yaml
send_pubkey = 1
client_private = client_key
client_public = client_cert
server_public = server_cert</pre>

And it's fully compatable with old style.