♲ Refactor configuration to use viper with context propagation

- Replace global ConfigPath and Overrides with viper-based configuration
- Add viper.New() to create configurable viper instances
- Store viper and unmarshaled Config struct in context for testability
- Add RetrieveFromContext and AddToContext helper functions
- Update files.Append to accept context and retrieve config from it
- Update formatters.Preferred and formatters.New to accept context
- Add PersistentPreRunE in CLI to create and configure viper instance
- Support -c flag for custom config file path
- Support -v flag for config value overrides
- Update all test files to create viper and add to context
- Remove unused config types and load functions
- Add viper as dependency with automatic env var support (MYLOG_*)

config/default.go

@@ -4,8 +4,6 @@ import (
 	"fmt"
 	"os"
 	fp "path/filepath"
-
-	"github.com/BurntSushi/toml"
 )
 
 const ConfigStr = `# Configuration for my-log
@@ -38,15 +36,13 @@ pretty_print = false
 
 `
 
+func DefaultPath() string {
+	conf, _ := os.UserConfigDir()
+	return fp.Join(conf, "my-log", "config.toml")
+}
+
 func DefaultStr() string {
 	home, _ := os.UserHomeDir()
 	inDir := fp.Join(home, "my-log")
 	return fmt.Sprintf(ConfigStr, inDir)
 }
-
-func DefaultConfig() (Config, error) {
-	s := DefaultStr()
-	c := Config{}
-	_, err := toml.Decode(s, &c)
-	return c, err
-}