Env File Parsing

[tommyhtran]

There are some differences between how the built-in Deno.env parses .env files and how @std/dotenv parses .env files. These differences should be documented at https://docs.deno.com/runtime/reference/env_variables/.

• Unquoted values with spaces
  • .env cannot be read if values contain spaces deno#21393
• Variable expansion
  • Built-in Deno.env parses $ENVVARIABLENAME for variable expansion
    • Could be escaped with a backslash character
  • @std/dotenv doesn't