add a Lock, LockGuard and printThreadInfo

* `Lock`: trivial wrapper for FreeRTOS binary semaphores
* `LockGuard`: RAII wrapper for using `Lock`
* `printThreadInfo`: helper for showing which core/FreeRTOS task we are
  running under

src/lock.cpp

@@ -0,0 +1,35 @@
+#include "lock.h"
+
+#include <cassert>
+
+namespace meshtastic
+{
+
+Lock::Lock()
+{
+    handle = xSemaphoreCreateBinary();
+    assert(handle);
+    assert(xSemaphoreGive(handle));
+}
+
+void Lock::lock()
+{
+    assert(xSemaphoreTake(handle, portMAX_DELAY));
+}
+
+void Lock::unlock()
+{
+    assert(xSemaphoreGive(handle));
+}
+
+LockGuard::LockGuard(Lock *lock) : lock(lock)
+{
+    lock->lock();
+}
+
+LockGuard::~LockGuard()
+{
+    lock->unlock();
+}
+
+} // namespace meshtastic