It's errors and fatals only

Ditch the concept of internal,
fatals are from templates,
errors are from ain.

Errors can be your fault
or the computers. Fatals
are exclusively yours.

Test plan:
* go run cmd/ain/main.go
  and verify error message
  still looks the same.

cmd/ain/main.go

@@ -9,8 +9,6 @@ import (
 	"strings"
 	"syscall"
 
-	"github.com/pkg/errors"
-
 	"github.com/jonaslu/ain/internal/app/ain"
 	"github.com/jonaslu/ain/internal/pkg/call"
 	"github.com/jonaslu/ain/internal/pkg/disk"
@@ -22,8 +20,8 @@ var gitSha = "develop"
 
 const bashSignalCaughtBase = 128
 
-func printInternalErrorAndExit(err error) {
-	formattedError := fmt.Sprintf("Error: %v", err.Error())
+func printErrorAndExit(err error) {
+	formattedError := fmt.Sprintf("Error: %s", err.Error())
 	fmt.Fprintln(os.Stderr, formattedError)
 	os.Exit(1)
 }
@@ -48,7 +46,7 @@ func main() {
 
 	if cmdParams.GenerateEmptyTemplate {
 		if err := disk.GenerateEmptyTemplates(); err != nil {
-			printInternalErrorAndExit(err)
+			printErrorAndExit(err)
 		}
 
 		return
@@ -66,17 +64,16 @@ func main() {
 	}
 
 	if err := disk.ReadEnvFile(cmdParams.EnvFile, cmdParams.EnvFile != ".env"); err != nil {
-		printInternalErrorAndExit(err)
+		printErrorAndExit(err)
 	}
 
 	localTemplateFileNames, err := disk.GetTemplateFilenames(cmdParams.TemplateFileNames)
 	if err != nil {
-		printInternalErrorAndExit(err)
+		printErrorAndExit(err)
 	}
 
 	if len(localTemplateFileNames) == 0 {
-		// !! TODO !! This is not an internal error
-		printInternalErrorAndExit(errors.New("Missing template file name(s)\n\nTry 'ain -h' for more information"))
+		printErrorAndExit(fmt.Errorf("missing template file name(s)\n\nTry 'ain -h' for more information"))
 	}
 
 	cancelCtx, cancel := context.WithCancel(context.Background())
@@ -94,7 +91,7 @@ func main() {
 	if err != nil {
 		checkSignalRaisedAndExit(assembledCtx, signalRaised)
 
-		printInternalErrorAndExit(err)
+		printErrorAndExit(err)
 	}
 
 	if fatal != "" {
@@ -109,7 +106,7 @@ func main() {
 
 	call, err := call.Setup(backendInput)
 	if err != nil {
-		printInternalErrorAndExit(err)
+		printErrorAndExit(err)
 	}
 
 	if cmdParams.PrintCommand {