Add support to .env files

[maurosergiosilva]

Refactor code so config files load env from .env files, so I can use just one config file for any enviroment.
.env files could be managed by dotenv
.env / .env.test need to be added to .gitignore, and only .env.example should be commited
if node_env = test, .env.test should be used instead of .env file
docs must be updated to reflect those changes.

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