Auto complete with space prefixed line (#46)

* auto-complete gets displayed even with space characters prefixing the line

* demo test back to chzyer;

complete_helper.go

@@ -73,7 +73,7 @@ func (p *PrefixCompleter) Do(line []rune, pos int) (newLine [][]rune, offset int
 }
 
 func Do(p PrefixCompleterInterface, line []rune, pos int) (newLine [][]rune, offset int) {
-	line = line[:pos]
+	line = runes.TrimSpaceLeft(line[:pos])
 	goNext := false
 	var lineCompleter PrefixCompleterInterface
 	for _, child := range p.GetChildren() {

runes.go

@@ -154,3 +154,14 @@ aggregate:
 	}
 	return
 }
+
+func (Runes) TrimSpaceLeft(in []rune) []rune {
+	firstIndex := len(in)
+	for i, r := range in {
+		if unicode.IsSpace(r) == false {
+			firstIndex = i
+			break
+		}
+	}
+	return in[firstIndex:]
+}