Set config from environment

[darth-veitcher]

Describe the problem At the moment (I believe) the config needs to be specified in the config.json file. It would be useful to be able to override k,v combinations from the environment (when they exist). This would assist with dockerising the script.

Describe any solutions you think might work After the file has been loaded merge the environment dict so that any set variables are overwritten in the config.