Assign narrow characters width 1

The narrow category applies to all ASCII characters, as well as
characters such as double angle brackets.  The tr11 annex says
that these characters are "always narrow and have explicit fullwidth
or wide counterparts", which I believe means they should be
assigned width one.

Previously, these characters were being assigned width 0.
I think before v0.0.5 they were being assigned width one,
but somewhere between v0.0.4 and v0.0.7 it changed to width 0
(maybe when introducing the generation script?).

runewidth.go

@@ -101,8 +101,10 @@ func NewCondition() *Condition {
 // See http://www.unicode.org/reports/tr11/
 func (c *Condition) RuneWidth(r rune) int {
 	switch {
-	case r < 0 || r > 0x10FFFF || inTables(r, nonprint, combining, narrow):
+	case r < 0 || r > 0x10FFFF || inTables(r, nonprint, combining):
 		return 0
+	case inTables(r, narrow):
+		return 1
 	case (c.EastAsianWidth && IsAmbiguousWidth(r)) || inTables(r, doublewidth):
 		return 2
 	default:

runewidth_test.go

@@ -164,6 +164,7 @@ var runewidthtests = []struct {
 	{'\u0300', 0, 0},
 	{'\u2028', 0, 0},
 	{'\u2029', 0, 0},
+	{'⟦', 1, 1}, // non-ASCII classified as "na" (narrow)
 }
 
 func TestRuneWidth(t *testing.T) {