Load config from environment

[bitbyt3r]

This code allows loading all config values from environment variables.
For example, the following sideboard.ini

[cherrypy]
server.socket_port = 80
server.socket_host = 0.0.0.0
server.socket_timeout = 1
tools.sessions.host = redis
tools.sessions.prefix = uber
tools.sessions.storage_type = redis

[loggers]
cherrypy.access = DEBUG

would become the following environment variables.

sideboard_cherrypy_server.socket_port=80
sideboard_cherrypy_server.socket_host=0.0.0.0
sideboard_cherrypy_server.socket_timeout=1
sideboard_cherrypy_tools.sessions.host=redis
sideboard_cherrypy_tools.sessions.prefix=uber
sideboard_cherrypy_tools.sessions.storage_type=redis
sideboard_loggers_cherrypy.access=DEBUG

Additionally, you can specify ini files to load via SIDEBOARD_CONFIG_FILES and <plugin name>_CONFIG_FILES with ; separated lists of files. These files can have either absolute paths or paths relative to their plugin root_dir.