Allow Prefix For Env Parse

[jbolda]

There are cases where we might want to provide an extra "factor" for the env parse as it is global. For example, having --debug is nice, short and memorable, but there might be multiple programs in our stack that are looking for a debug flag. As another example, one might have multiple simulators, each with a config, but they all have a --port option. These situations mostly lend themselves to env and config file parsing.

[cowboyd]

which environment variable route uses will be determined by the env() combinator. E.g.

option(
  name("debug"),
  env("APP_DEBUG")
)

Normally, it would match DEBUG, but with an explicit tag, it will instead look for APP_DEBUG

if it is nested in a route, the routes prefix will be already added.

Feel free to re-open if this continues to be an issue.