Fix forward reference to textPort

This Pull Request fixes the following errors on DMD32 2.063 on Windows.

```D
// sample.d
import dio.port;

void main() {
  dout.writeln("Hello!");
}
```

```
>dmd -IZ:\dio sample.d
Z:\dio\dio\port.d(252): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) forward reference to template textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte))
Z:\dio\dio\port.d(108): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) cannot deduce template function from argument types !()(StdIo)
Z:\dio\dio\port.d(252): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) forward reference to template textPort(Dev)(Dev device) if (isSomeChar!(DeviceEleme
ntType!(Dev)) || is(DeviceElementType!(Dev) == ubyte))
Z:\dio\dio\port.d(109): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) cannot deduce template function from argument types !()(StdIo)
Z:\dio\dio\port.d(252): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) forward reference to template textPort(Dev)(Dev device) if (isSomeChar!(DeviceEleme
ntType!(Dev)) || is(DeviceElementType!(Dev) == ubyte))
Z:\dio\dio\port.d(110): Error: template dio.port.textPort(Dev)(Dev device) if (isSomeChar!(DeviceElementType!(Dev)) || is(DeviceElementType!(Dev) == ubyte)) cannot deduce template function from argument types !()(StdIo)
```