Document compatibility with Amazon EC2 and how to use boto library

Document the compatibility of the nova-api endpoint with Amazon EC2. This includes:

- Which API calls are supported (partially documented right now at http://wiki.openstack.org/Nova/EucalyptusFeatureComparison although possibly out of date)
- how compatible the metadata service is
- Any differences in the content of the data structures returned. (For example, I ran into the "architecture" field not being set and the name set to "None" when querying images using the EPI).

Should also document how to use boto to connect to the endpoint. For example (and I'm not even 100% sure this is correct:

import boto.ec2
region_name = "My internal cloud"

endpoint = "192.168.2.10" # Example endpoint IP
access_key = ... # Describe how to determine the access key
secret_key = ... # Describe how to determine the secret key

# These are the defaults, at least for Diablo
port = 8773
path = "/services/Cloud"
is_secure = False # endpoint does not use SSL by default

region = boto.ec2.regioninfo.RegionInfo(region_name, endpoint)
connection = boto.ec2.connect_ec2(access_key, secret_key, region=region, port=port, path=path, is_secure=is_secure)