mda-lmtp: Add a very basic MDA that uses LMTP to do the mail delivery.

mda-lmtp is a very basic MDA that uses LMTP to do the mail delivery.

It takes command line arguments similar to maildrop or procmail, reads an
email via standard input, and sends it over the given LMTP server.
Supports connecting to LMTP servers over UNIX sockets and TCP.

Since chasquid does not support direct LMTP local delivery, this can be
used as a workaround instead.

Example of use:
$ mda-lmtp --addr localhost:1234 -f juan@casa -d jose < email

cmd/mda-lmtp/test_tcp_success.cmy

@@ -0,0 +1,32 @@
+
+nc tcp_listen localhost:14932
+
+mda |= ./mda-lmtp --addr=localhost:14932 -f from -d to < .data
+
+nc -> 220 Hola desde expect
+
+nc <~ LHLO .*
+nc -> 250-Bienvenido!
+nc -> 250 Contame...
+
+nc <- MAIL FROM:<from>
+nc -> 250 Aja
+
+nc <- RCPT TO:<to>
+nc -> 250 Aja
+
+nc <- DATA
+nc -> 354 Dale
+
+nc <- Subject: test
+nc <-
+nc <- This is a test.
+nc <- .
+
+nc -> 250 Recibido
+
+nc <- QUIT
+nc -> 221 Chauchas
+
+mda wait 0
+