Bugfixes (#13)

* several fixes:

- fix #9 + #10: switched to koanf module and dropped support for HCL
- fix #11: disabling colors on windows
- fix #12: fixed race condition in go routine call inside for loop,
  images had been downloaded multiple times
- remove hcl support and use toml format (same thing, better parser)
- update documentation and example config on TOML format of config file
- use Config as arg instead of singular args
- use x/errgroup instead of sync.Waitgroup inside image download loop

---------

Co-authored-by: Thomas von Dein <tom@vondein.org>

util.go

@@ -22,6 +22,9 @@ import (
 	"errors"
 	"os"
 	"os/exec"
+	"runtime"
+
+	"github.com/mattn/go-isatty"
 )
 
 func Mkdir(dir string) error {
@@ -53,3 +56,13 @@ func man() error {
 
 	return nil
 }
+
+// returns TRUE if stdout is NOT a tty or windows
+func IsNoTty() bool {
+	if runtime.GOOS == "windows" || !isatty.IsTerminal(os.Stdout.Fd()) {
+		return true
+	}
+
+	// it is a tty
+	return false
+}