Add configuration to support broker SSL

Possibly implements #154, if my assumptions about the implementation are
correct.

broker.go

@@ -1,6 +1,7 @@
 package sarama
 
 import (
+	"crypto/tls"
 	"fmt"
 	"io"
 	"net"
@@ -68,7 +69,15 @@ func (b *Broker) Open(conf *Config) error {
 	go withRecover(func() {
 		defer b.lock.Unlock()
 
-		b.conn, b.connErr = net.DialTimeout("tcp", b.addr, conf.Net.DialTimeout)
+		dialer := &net.Dialer{
+			Timeout: conf.Net.DialTimeout,
+		}
+
+		if conf.Net.TLS.Enable {
+			b.conn, b.connErr = tls.DialWithDialer(dialer, "tcp", b.addr, conf.Net.TLS.Config)
+		} else {
+			b.conn, b.connErr = dialer.Dial("tcp", b.addr)
+		}
 		if b.connErr != nil {
 			b.conn = nil
 			atomic.StoreInt32(&b.opened, 0)

config.go

@@ -1,6 +1,9 @@
 package sarama
 
-import "time"
+import (
+	"crypto/tls"
+	"time"
+)
 
 // Config is used to pass multiple configuration options to Sarama's constructors.
 type Config struct {
@@ -12,6 +15,11 @@ type Config struct {
 		DialTimeout  time.Duration // How long to wait for the initial connection to succeed before timing out and returning an error (default 30s).
 		ReadTimeout  time.Duration // How long to wait for a response before timing out and returning an error (default 30s).
 		WriteTimeout time.Duration // How long to wait for a transmit to succeed before timing out and returning an error (default 30s).
+
+		TLS struct {
+			Enable bool        // Whether or not to use TLS when connecting to the broker (defaults to false).
+			Config *tls.Config // The TLS configuration to use for secure connections if enabled (defaults to nil).
+		}
 	}
 
 	// Metadata is the namespace for metadata management properties used by the Client, and shared by the Producer/Consumer.