binds: allow to bind a command to < and >

Allow to bind to < and > by using \< and \> in binds.conf. Ensure that
the single \ can still be properly used to bind to other commands.

For example, the following binds would work now:
\< = :prev-tab<Enter>
\> = :next-tab<Enter>
\ = :filter<space>

Fixes: https://todo.sr.ht/~rjarry/aerc/37
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Tested-by: Sebastian LaVine <mail@smlavine.com>
Acked-by: Robin Jarry <robin@jarry.cc>

config/bindings.go

@@ -199,6 +199,14 @@ func ParseKeyStrokes(keystrokes string) ([]KeyStroke, error) {
 			}
 		case '>':
 			return nil, errors.New("Found '>' without '<'")
+		case '\\':
+			tok, _, err = buf.ReadRune()
+			if err == io.EOF {
+				tok = '\\'
+			} else if err != nil {
+				return nil, err
+			}
+			fallthrough
 		default:
 			strokes = append(strokes, KeyStroke{
 				Modifiers: tcell.ModNone,