Caleb

Fixed window roller expand env var

2

This PR implements expanding env vars in file patterns in `FixedWindowRoller` as requested here https://github.com/estk/log4rs/issues/280 .

This pull request does three things. - Fixes the type on `expectErr` in `BaseResult` - Adds `expectErr` tests in the ok and err test files. - Updates the Readme to...