Configure application with environment

[zfletch]

Using the Flask-Env library, allow overwriting configuration files with environment variables. This is done by passing ENV as an argument to run.py and putting DIGMILL_ before a particular configuration option.

For example: env DIGMILL_MONGO_HOST=mongo python run.py config.cfg ENV will use the configuration specified in config.cfg but overwrite the MONGO_HOST option.

I think this is the ideal solution. It provides a lot of flexibility without making major changes, since:

• deployment scripts don't have to be changed to use the environment instead of a .cfg files
• the application can be deployed with environment variable configuration if it needs to be (for example, any PaaS that requires 12 factor apps)
• the default configuration is shared in both cases.

[coveralls]

Coverage increased (+0.03%) to 86.236% when pulling 6939ed532571dfd16d2a3a38e9aa2537c49ac26f on configure-with-env into 7786138f2c5d59dc9293908c9ab5ffb21f15cf24 on master.