Various HAL enhancements. (#182)

* Add <D SERVO vpin position> command

Allow a PWM servo to be driven to any arbitrary position.

* Enhancements for HAL drivers

Add state change notification for external GPIO module drivers;
Allow drivers to be installed statically by declaration (as an alternative to the 'create' call).

* Create IO_HCSR04.h

HAL driver for HC-SR04 ultrasonic distance sensor (sonar).

* Enable servo commands in NO-HAL mode, but return error.

Avoid compile errors in RMFT.cpp when compiled with basic HAL by including the Turnout::createServo function as a stub that returns NULL.

* Update IO_HCSR04.h

Minor changes

* Change <D SERVO>

Give the <D SERVO> command an optional parameter of the profile.  For example, <D SERVO 100 200 3> will slowly move the servo on pin 100 to PWM position corresponding to 200.  If omitted, the servo will move immediately (no animation).

* IODevice (HAL) changes

1) Put new devices on the end of the chain instead of the beginning.  This will give better performance for devices created first (ArduinoPins and extender GPIO devices, typically).
2) Remove unused functions.

* Update IO_HCSR04.h

Allow thresholds for ON and OFF to be separately configured at creation.

* Update IODevice.cpp

Fix compile error on IO_NO_HAL minimal HAL version.

* Update IO_PCA9685.cpp

Remove unnecessary duplicated call to min() function.

Turnouts.cpp

@@ -18,7 +18,7 @@
  *  You should have received a copy of the GNU General Public License
  *  along with CommandStation.  If not, see <https://www.gnu.org/licenses/>.
  */
-#define EESTOREDEBUG 
+//#define EESTOREDEBUG 
 #include "defines.h"
 #include "Turnouts.h"
 #include "EEStore.h"
@@ -72,13 +72,11 @@ void Turnout::print(Print *stream){
       // VPIN Digital output
       StringFormatter::send(stream, F("<H %d VPIN %d %d>\n"), data.id, data.vpinData.vpin, state);
       break;
-#ifndef IO_NO_HAL
     case TURNOUT_SERVO:
       // Servo Turnout
       StringFormatter::send(stream, F("<H %d SERVO %d %d %d %d %d>\n"), data.id, data.servoData.vpin, 
         data.servoData.activePosition, data.servoData.inactivePosition, data.servoData.profile, state);
       break;
-#endif
     default:
       break;
   }
@@ -89,9 +87,6 @@ void Turnout::print(Print *stream){
 //   Returns false if turnout not found.
 
 bool Turnout::activate(int n, bool state){
-#ifdef EESTOREDEBUG
-  DIAG(F("Turnout::activate(%d,%d)"),n,state);
-#endif
   Turnout * tt=get(n);
   if (!tt) return false;
   tt->activate(state);
@@ -136,11 +131,11 @@ void Turnout::activate(bool state) {
         DCC::setAccessory((((data.dccAccessoryData.address-1) >> 2) + 1), 
           ((data.dccAccessoryData.address-1) & 3), state);
         break;
-#ifndef IO_NO_HAL
       case TURNOUT_SERVO:
+#ifndef IO_NO_HAL
         IODevice::write(data.servoData.vpin, state);
-        break;
 #endif
+        break;
       case TURNOUT_VPIN:
         IODevice::write(data.vpinData.vpin, state);
         break;
@@ -205,12 +200,10 @@ void Turnout::load(){
       case TURNOUT_LCN:
         // LCN turnouts are created when the remote device sends a message.
         break;
-#ifndef IO_NO_HAL
       case TURNOUT_SERVO:
         tt=createServo(data.id, data.servoData.vpin, 
           data.servoData.activePosition, data.servoData.inactivePosition, data.servoData.profile, lastKnownState);
         break;
-#endif
       case TURNOUT_VPIN:
         tt=createVpin(data.id, data.vpinData.vpin, lastKnownState);  // VPIN-based turnout
         break;
@@ -294,11 +287,11 @@ Turnout *Turnout::createVpin(int id, VPIN vpin, uint8_t state){
   return(tt);
 }
 
-#ifndef IO_NO_HAL
 ///////////////////////////////////////////////////////////////////////////////
 // Method for creating a Servo Turnout, e.g. connected to PCA9685 PWM device.
 
 Turnout *Turnout::createServo(int id, VPIN vpin, uint16_t activePosition, uint16_t inactivePosition, uint8_t profile, uint8_t state){
+#ifndef IO_NO_HAL
   if (activePosition > 511 || inactivePosition > 511 || profile > 4) return NULL;
 
   Turnout *tt=create(id);
@@ -317,8 +310,11 @@ Turnout *Turnout::createServo(int id, VPIN vpin, uint16_t activePosition, uint16
     return NULL;
   }
   return(tt);
-}
+#else
+  (void)id; (void)vpin; (void)activePosition; (void)inactivePosition; (void)profile; (void)state;  // avoid compiler warnings
+  return NULL;
 #endif
+}
 
 ///////////////////////////////////////////////////////////////////////////////
 // Support for <T id SERVO pin activepos inactive pos profile>
@@ -326,14 +322,12 @@ Turnout *Turnout::createServo(int id, VPIN vpin, uint16_t activePosition, uint16
 // and <T id VPIN pin>
 
 Turnout *Turnout::create(int id, int params, int16_t p[]) {
-#ifndef IO_NO_HAL
   if (p[0] == HASH_KEYWORD_SERVO) { // <T id SERVO n n n n>
     if (params == 5)
       return createServo(id, (VPIN)p[1], (uint16_t)p[2], (uint16_t)p[3], (uint8_t)p[4]);
     else  
       return NULL;
   } else 
-#endif
   if (p[0] == HASH_KEYWORD_VPIN) { // <T id VPIN n>
     if (params==2)
       return createVpin(id, p[1]);
@@ -350,11 +344,9 @@ Turnout *Turnout::create(int id, int params, int16_t p[]) {
   } else if (params==2) { // <T id n n> for DCC or LCN
     return createDCC(id, p[0], p[1]);
   } 
-#ifndef IO_NO_HAL
   else if (params==3) { // legacy <T id n n n> for Servo
     return createServo(id, (VPIN)p[0], (uint16_t)p[1], (uint16_t)p[2]);
   }
-#endif
 
   return NULL;
 }