add back list command, print instances in a pretty table

Here's what it looks like:

```
$ pairhost list
+-------------------------------------------------------+------------+---------+-----------+-------------------------+--------------+--------------------------------------------+
| name                                                  | id         | state   | type      | created_at              | image_id     | dns_name                                   |
+-------------------------------------------------------+------------+---------+-----------+-------------------------+--------------+--------------------------------------------+
| MDE Tolven Development 10                             | i-2d58ec43 | stopped | m1.large  | 2011-06-21 14:05:56 UTC | ami-c039c6a9 |                                            |
| MDE Tolven Demo                                       | i-03c1f16d | running | m1.large  | 2011-07-25 13:03:00 UTC | ami-daf803b3 | ec2-50-16-16-55.compute-1.amazonaws.com    |
| HCVS Permanent Demo (Rails)                           | i-bfe81edc | running | m1.large  | 2011-10-25 15:51:24 UTC | ami-fd589594 | ec2-50-19-190-61.compute-1.amazonaws.com   |
| HCVS Permanent Demo (FMS) (i2demo.icsl.net)           | i-a7bd43c4 | running | m1.large  | 2011-10-26 13:40:41 UTC | ami-fd589594 | ec2-107-21-126-39.compute-1.amazonaws.com  |
| BC                                                    | i-14d53776 | running | m1.large  | 2012-04-26 17:21:49 UTC | ami-9360affa | ec2-23-22-24-95.compute-1.amazonaws.com    |
| JD SP (WebAssign Dev)                                 | i-87eb7be2 | stopped | m1.large  | 2012-04-27 13:45:44 UTC | ami-9360affa |                                            |
| Vivisimo Dev (RS/AD/LD)                               | i-ff8f109a | stopped | m1.large  | 2012-03-16 20:00:52 UTC | ami-9360affa |                                            |
| Gitolite - Mckinsey Git Hosting                       | i-a0e0efc4 | running | m1.small  | 2012-03-29 18:49:46 UTC | ami-9360affa | ec2-184-73-35-14.compute-1.amazonaws.com   |
| Nixon-Neufeld Clambake                                | i-65698402 | stopped | m1.large  | 2012-04-05 14:02:21 UTC | ami-9360affa |                                            |
| DevOps Dev (GH)                                       | i-7baa461c | running | m1.large  | 2012-04-27 18:42:12 UTC | ami-9360affa | ec2-50-17-141-140.compute-1.amazonaws.com  |
| DevOps Dev (LD SU)                                    | i-518e2236 | running | m1.large  | 2012-04-26 14:22:54 UTC | ami-9360affa | ec2-107-21-164-102.compute-1.amazonaws.com |
| Greylog2 server                                       | i-ba2d9bdd | stopped | m1.small  | 2012-04-14 02:26:15 UTC | ami-bf75abd6 |                                            |
| Big Data & Datomic (LV)                               | i-9477c6f3 | stopped | m1.xlarge | 2012-04-21 16:06:06 UTC | ami-9360affa |                                            |
| LV CA                                                 | i-2ef36d49 | stopped | m1.large  | 2012-04-26 13:18:14 UTC | ami-9360affa |                                            |
| JR (2012-04)                                          | i-9091f6f7 | stopped | m1.large  | 2012-04-23 15:03:20 UTC | ami-9360affa |                                            |
| Metron: Metrics and Monitoring server                 | i-dac9a8bd | running | m1.large  | 2012-04-17 19:52:48 UTC | ami-fd589594 | ec2-23-23-205-193.compute-1.amazonaws.com  |
| MonitoredApp1 qa (AR GH)                              | i-14066673 | stopped | m1.large  | 2012-04-17 20:27:38 UTC | ami-fd589594 |                                            |
| No Name                                               | i-8ea7cee9 | stopped | m1.large  | 2012-04-18 17:44:10 UTC | ami-fd589594 |                                            |
| bv - word magic                                       | i-5ca4cc3b | stopped | m1.large  | 2012-04-25 13:54:41 UTC | ami-9360affa |                                            |
| Thinkrelevance new_one                                | i-fcffab9b | stopped | m1.large  | 2012-04-23 19:31:05 UTC | ami-fd589594 |                                            |
| Hello hello                                           | i-feacfd99 | running | m1.large  | 2012-04-24 00:13:05 UTC | ami-fd589594 | ec2-184-73-101-4.compute-1.amazonaws.com   |
| Hello hello                                           | i-06d38261 | running | m1.large  | 2012-04-24 00:15:56 UTC | ami-fd589594 | ec2-23-20-194-58.compute-1.amazonaws.com   |
| Magma Dev 2 (BA MF RO SS)                             | i-862c72e1 | stopped | m1.large  | 2012-04-26 13:14:25 UTC | ami-9360affa |                                            |
| mygroup-e4a0fe83                                      | i-e4a0fe83 | running | t1.micro  | 2012-04-24 19:05:56 UTC | ami-77e50b1e | ec2-184-73-50-183.compute-1.amazonaws.com  |
| qa-opp-web-90fba5f7                                   | i-90fba5f7 | running | m1.small  | 2012-04-24 19:28:23 UTC | ami-4a0df923 | ec2-23-20-211-108.compute-1.amazonaws.com  |
| Hello ec2                                             | i-40e5bb27 | running | m1.large  | 2012-04-24 19:37:47 UTC | ami-fd589594 | ec2-50-16-43-167.compute-1.amazonaws.com   |
| GH LK DEBUG 1                                         | i-403b1327 | stopped | m1.large  | 2012-04-26 18:08:40 UTC | ami-fd589594 |                                            |
| GH LK DEBUG 2                                         | i-800d25e7 | stopped | m1.large  | 2012-04-26 14:59:57 UTC | ami-fd589594 |                                            |
| debug3-opp-web-90be95f7                               | i-90be95f7 | running | m1.small  | 2012-04-26 18:24:36 UTC | ami-4a0df923 | ec2-107-21-172-93.compute-1.amazonaws.com  |
| debug3-opp-web-fa8ba09d                               | i-fa8ba09d | running | m1.small  | 2012-04-26 18:30:21 UTC | ami-4a0df923 | ec2-107-22-105-140.compute-1.amazonaws.com |
| qa-opp-web-c42f05a3                                   | i-c42f05a3 | running | m1.small  | 2012-04-26 19:28:49 UTC | ami-4a0df923 | ec2-107-20-74-159.compute-1.amazonaws.com  |
| AppForCi Nightly Build Testing - 2012-04-27 01:44:40  | i-5a3d0b3d | stopped | m1.large  | 2012-04-27 05:44:43 UTC | ami-fd589594 |                                            |
| AppForCi Nightly Build Testing - 2012-04-27 02:00:28  | i-f4152393 | stopped | m1.large  | 2012-04-27 06:00:31 UTC | ami-fd589594 |                                            |
| Russ/Clinton pairhost                                 | i-52192a35 | running | m1.large  | 2012-04-27 14:12:24 UTC | ami-9360affa | ec2-107-20-47-201.compute-1.amazonaws.com  |
+-------------------------------------------------------+------------+---------+-----------+-------------------------+--------------+--------------------------------------------+
34 rows in set
```

I could also add options to query rows (by name) or sort by a field. Ping me if you want to tweak the table some.