Version 1.4.9

Note: If there are no special circumstances, this will be the last version of v1.4.x, starting from v1.5.x, we bumped the minimum go version to go1.18.

• Add GetHighPriorityLevels and GetLowPriorityLevels util function.
• Add Log.IsLevelEnabled(Level) and Log.Is<LevelName>LevelEnabled() to detect whether the log level is enabled.
• Add Logger.SetLevelString and Logger.ForceSetLevelString to support setting log level from string.
• Add Log.WithFieldPairs(key, value, key, value, ...) method to attach tabulated key-value pair fields to log.
• Some internal performance improvements and stability upgrades.
• Migrate CI to Github Actions (See #13).