Add Support configuration from environment variables.

[thomasf]

At least relevant for the web service. The requirements are guided by my docker containerisation project.

I'm thinking along the lines of changing

ipasn.hostname = 'redis'
ipasn.port=6379

To something along the lines of:

ipasn.hostname = os.environ.get('IPASN_REDIS_HOST', 'redis')
ipasn.port=os.environ.get('IPASN_REDIS_PORT', 6379)

Also adding this as an alternative to the configparser config file would make it easy to handle from a docker point of view..

If you find this idea useful I can submit a pull request.

[thomasf]

I'll just make a go port of everything