EC2 pricing tie-in

Hi, I'm not sure if you are accepting pull requests but I've added a little extra information to the ec2 instance types to: 

1. Allow programatic access to instance pricing. 
2. Group instances by category

This is just preliminary, I can clean it up or change this before you pull.

This is related to Issue #6

I have included an example script `costs.py` to serve as an example of how to use the new metadata with the amazon json files from:

 * `http://aws.amazon.com/ec2/pricing/json/<OS>-<RESERVATION_TYPE_CODE>.json`

You may need to `pip install requirements`  first:
```
$python costs.py us-east

Cluster Compute Instances
 + Eight Extra Large (cc2.8xlarge)      |   $2.400 / hour
 + Quadruple Extra Large (cc1.4xlarge)  |   $1.300 / hour

Cluster GPU Instances
 + Quadruple Extra Large (cg1.4xlarge)  |   $2.100 / hour

High-CPU Instances
 + Extra Large (c1.xlarge)              |   $0.580 / hour
 + Medium (c1.medium)                   |   $0.145 / hour

High-I/O Instances
 + Quadruple Extra Large (hi1.4xlarge)  |   $3.100 / hour

High-Memory Cluster Instances
 + Eight Extra Large (cr1.8xlarge)      |   $3.500 / hour

High-Memory Instances
 + Extra Large (m2.xlarge)              |   $0.410 / hour
 + Quadruple Extra Large (m2.4xlarge)   |   $1.640 / hour
 + Double Extra Large (m2.2xlarge)      |   $0.820 / hour

High-Storage Instances
 + Eight Extra Large (hs1.8xlarge)      |   $4.600 / hour

Micro Instances
 + Micro (t1.micro)                     |   $0.020 / hour

Second Generation Standard Instances
 + Double Extra Large (m3.2xlarge)      |   $1.000 / hour
 + Extra Large (m3.xlarge)              |   $0.500 / hour

Standard Instances
 + Medium (m1.medium)                   |   $0.120 / hour
 + Large (m1.large)                     |   $0.240 / hour
 + Small (Default) (m1.small)           |   $0.060 / hour
 + Extra Large (m1.xlarge)              |   $0.480 / hour
```