Add function to wait for all buttons released

New function waitNoButtons() replaces the code at the end of begin()
that waits for all buttons to be released. This is to make it easier
to add back this functionality when using boot() in place of begin().

README.md

@@ -187,10 +187,7 @@ void Arduboy2Base::begin()
 
   bootLogo();
 
-  // wait for all buttons to be released
+  waitNoButtons(); // wait for all buttons to be released
-  do {
-    delay(50);
-  } while (buttonsState());
 }
 ```
 
@@ -213,13 +210,10 @@ For example: Let's say a sketch has its own code to enable, disable and save the
 
 //  bootLogo();
 
-  // wait for all buttons to be released
+//  waitNoButtons(); // wait for all buttons to be released
-  do {
-    delay(50);
-  } while (arduboy.buttonsState());
 ```
 
-This saves whatever code *blank()*, *systemButtons()* and *bootLogo()* would use.
+This saves whatever code *blank()*, *systemButtons()*, *bootLogo()* and *waitNoButtons()* would use.
 
 There are a few functions provided that are roughly equivalent to the standard functions used by *begin()* but which use less code space.
 

keywords.txt

@@ -95,6 +95,7 @@ setTextWrap	KEYWORD2
 SPItransfer	KEYWORD2
 systemButtons	KEYWORD2
 toggle	KEYWORD2
+waitNoButtons	KEYWORD2
 width	KEYWORD2
 writeShowUnitNameFlag	KEYWORD2
 writeUnitID	KEYWORD2

src/Arduboy2.cpp

@@ -47,10 +47,7 @@ void Arduboy2Base::begin()
 //  bootLogoSpritesSelfMasked();
 //  bootLogoSpritesOverwrite();
 
-  // wait for all buttons to be released
+  waitNoButtons(); // wait for all buttons to be released
-  do {
-    delayShort(50);
-  } while (buttonsState());
 }
 
 void Arduboy2Base::flashlight()
@@ -174,6 +171,13 @@ void Arduboy2Base::bootLogoShell(void (*drawLogo)(int16_t))
 // Virtual function overridden by derived class
 void Arduboy2Base::bootLogoExtra() { }
 
+// wait for all buttons to be released
+void Arduboy2Base::waitNoButtons() {
+  do {
+    delayShort(50); // simple button debounce
+  } while (buttonsState());
+}
+
 /* Frame management */
 
 void Arduboy2Base::setFrameRate(uint8_t rate)

src/Arduboy2.h

@@ -334,6 +334,25 @@ class Arduboy2Base : public Arduboy2Core
   // information after the logo stops scrolling down.
   virtual void bootLogoExtra();
 
+  /** \brief
+   * Wait until all buttons have been released.
+   *
+   * \details
+   * This function is called by `begin()` and can be called by a sketch
+   * after `boot()`.
+   *
+   * It won't return unless no buttons are being pressed. A short delay is
+   * performed each time before testing the state of the buttons to do a
+   * simple button debounce.
+   *
+   * This function is called at the end of `begin()` to make sure no buttons
+   * used to perform system start up actions are still being pressed, to
+   * prevent them from erroneously being detected by the sketch code itself.
+   *
+   * \see begin() boot()
+   */
+  void waitNoButtons();
+
   /** \brief
    * Clear the display buffer.
    *