With no data to read, don't let liblber treat us as closed

Not sure what to do when the socket really gets closed.
Allocate a client/server context

We are going to be a client too.
Cleanup whitespace
Remove dead code
Move stuff to imap.c
Initialize the listener inside imap.c
Add config prototypes
Introduce config file and command-line options.
Add module prototypes
Add module implementation and make imap a module.
Do not use global config in modules
Plug two leaks.

Should probably have ctx freeing function though.
Style changes
Stop reading from client while connecting to the server
Do not allow TLS layer nesting
Register the STARTTLS handler only when configured
Be a bit more IMAP4rev1 compliant
Remove old example
Outline for ldap resolution
Change Makefile style

A prelude to proper dependency tracking.