Allocate class instances statically

Avoiding dynamic allocation saves some bookkeeping, but mainly
it lets Platform.IO output a more faithful evaluation of the RAM
requirements for the firmware.

src/ayab/main.cpp

@@ -32,28 +32,25 @@
 #include "solenoids.h"
 #include "tester.h"
 
-// Global definitions: references elsewhere must use `extern`.
-// Each of the following is a pointer to a singleton class
-// containing static methods.
-constexpr GlobalBeeper    *beeper;
-constexpr GlobalCom       *com;
-constexpr GlobalEncoders  *encoders;
-constexpr GlobalFsm       *fsm;
-constexpr GlobalKnitter   *knitter;
-constexpr GlobalSolenoids *solenoids;
-constexpr GlobalTester    *tester;
-
 // Initialize static members.
 // Each singleton class contains a pointer to a static instance
 // that implements a public interface. When testing, a pointer
 // to an instance of a mock class can be substituted.
-BeeperInterface    *GlobalBeeper::m_instance    = new Beeper();
-ComInterface       *GlobalCom::m_instance       = new Com();
-EncodersInterface  *GlobalEncoders::m_instance  = new Encoders();
-FsmInterface       *GlobalFsm::m_instance       = new Fsm();
-KnitterInterface   *GlobalKnitter::m_instance   = new Knitter();
-SolenoidsInterface *GlobalSolenoids::m_instance = new Solenoids();
-TesterInterface    *GlobalTester::m_instance    = new Tester();
+Beeper _Beeper;
+Com _Com;
+Encoders _Encoders;
+Fsm _Fsm;
+Knitter _Knitter;
+Solenoids _Solenoids;
+Tester _Tester;
+
+BeeperInterface    *GlobalBeeper::m_instance    = &_Beeper;
+ComInterface       *GlobalCom::m_instance       = &_Com;
+EncodersInterface  *GlobalEncoders::m_instance  = &_Encoders;
+FsmInterface       *GlobalFsm::m_instance       = &_Fsm;
+KnitterInterface   *GlobalKnitter::m_instance   = &_Knitter;
+SolenoidsInterface *GlobalSolenoids::m_instance = &_Solenoids;
+TesterInterface    *GlobalTester::m_instance    = &_Tester;
 
 /*!
  * Setup - do once before going to the main loop.