Environment variables

Env provide small set of functions to work with environment variables. Like this:

Env.LoadFile("/path/to/.env");
var secret = Env.GetRequired("SECRET");

Env.LoadFile will set environment variables if file exists.

Env.GetRequired get environment variable, but throw if one isn't found. It's rare time when I decided to use throw. I think environment variables should be loaded at the start of program. If variable isn't found then we can't start program.