Release version 0.5.0

• Update from log 0.3 to log 0.4. Both log versions are interoperable, but line numbers from libraries using 0.4 won't show up in binaries with recievers using log 0.4.
  • To clarify: both fern 0.4 and 0.5 will work perfectly with all libraries, but line numbers will always be 0 if you use fern 0.4 and log 0.4.
• Remove fern::FernLog. With log 0.4, log records can be constructed directly, and fern loggers can now recieve just a record rather than a record and the formatted display string.
• Notable changes in the log crate: log::LogLevel is renamed to log::Level, and log::LogLevelFilter is renamed to log::LevelFilter.
• fern::color::ColoredLogLevelConfig has been renamed to fern::color::ColoredLevelConfig to match log crate renamings.
• fern tests have been greatly simplified with the new support for creating log records manually. it's now possible to just run "cargo test" and test all of fern's functionality.