Use absolute paths where possible

bingobot blindly uses the shell's working dir to write logs and read
configs. This change introduces the following changes:

1. start.sh now determines the project root's absolute path before
   reading the token file and starting the app.
2. the config package now determine's the executable's working directory
   (rather than assuming it's the same as the shell's) before loading
   configs. It also now exposes this for use in other packages.
3. the logging package now uses config.GetWorkingDir() to determine
   where to write logs.

internal/config/config.go

@@ -2,6 +2,8 @@ package config
 
 import (
 	"fmt"
+	"os"
+	"path/filepath"
 
 	"github.com/spf13/viper"
 )
@@ -36,16 +38,29 @@ type AppConfig struct {
 }
 
 var config *AppConfig
+var workingDir string
 
 func init() {
 	setDefaults()
 	viper.Unmarshal(&config)
+
+	ex, err := os.Executable()
+
+	if err != nil {
+		panic(fmt.Errorf("failed to get path of executable (self): %v", err))
+	}
+
+	workingDir = filepath.Dir(ex)
 }
 
 func Get() *AppConfig {
 	return config
 }
 
+func GetWorkingDir() string {
+	return workingDir
+}
+
 func GetDefaultConfig() *AppConfig {
 	var config *AppConfig
 	setDefaults()
@@ -62,7 +77,7 @@ func Init() error {
 
 	viper.SetConfigName("config")
 	viper.SetConfigType("yaml")
-	viper.AddConfigPath(".")
+	viper.AddConfigPath(workingDir)
 
 	err := viper.ReadInConfig()
 	if err != nil {