add support for ConnWithTimeout

[letsfire]

For #17

[mna]

Thanks, looks good! I'd like to see a couple tests before merging, one for DoWithTimeout and another for ReceiveWithTimeout. What I have in mind to test this is:

• Create a cluster with the DialOptions specifying a DialReadTimeout of 1s
• Call Do with the BLPOP X 2 (i.e. block on popping list X for 2 seconds), this should fail due to the read timeout (1s)
• Call DoWithTimeout with a timeout of 3s, with the BLPOP X 2 command, this should succeed (and return nil because the list is empty)

Similarly for ReceiveWithTimeout, call Send instead of Do to send the BPOP command, and then Receive should fail due to the read timeout while ReceiveWithTimeout should succeed.

[letsfire]

@mna I tested the code as you said. My english is poor, i hope i did the right things

[mna]

Hey thanks! No worries, you did a great job, I'm just gonna tweak the test a little bit for the Receive part but otherwise everything looks great, I should able to merge today!