Minimize header use, move Ticker function definitions into cpp file (#6496)

* Backport from ESP32

* Use new library layout (.../src)

* Cleanup test case.

* C++ style cast required.

* Whitespace

* Inlining via header has better baseline ROM footprint.

* Reordered functions for better code-compare to master

* Reduces ROM footprint some more.

* Avoid unnecessary parameter passing - refactoring, same generated footprint.

* Reformat example sources

libraries/Ticker/src/Ticker.cpp

@@ -0,0 +1,71 @@
+/*
+  Ticker.cpp - esp8266 library that calls functions periodically
+
+  Copyright (c) 2014 Ivan Grokhotkov. All rights reserved.
+  This file is part of the esp8266 core for Arduino environment.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#include "c_types.h"
+#include "eagle_soc.h"
+#include "osapi.h"
+
+#include "Ticker.h"
+
+Ticker::Ticker()
+    : _timer(nullptr) {}
+
+Ticker::~Ticker()
+{
+    detach();
+}
+
+void Ticker::_attach_ms(uint32_t milliseconds, bool repeat, callback_with_arg_t callback, void* arg)
+{
+    if (_timer)
+    {
+        os_timer_disarm(_timer);
+    }
+    else
+    {
+        _timer = &_etsTimer;
+    }
+
+    os_timer_setfn(_timer, callback, arg);
+    os_timer_arm(_timer, milliseconds, repeat);
+}
+
+void Ticker::detach()
+{
+    if (!_timer)
+        return;
+
+    os_timer_disarm(_timer);
+    _timer = nullptr;
+    _callback_function = nullptr;
+}
+
+bool Ticker::active() const
+{
+    return _timer;
+}
+
+void Ticker::_static_callback(void* arg)
+{
+    Ticker* _this = reinterpret_cast<Ticker*>(arg);
+    if (_this && _this->_callback_function)
+        _this->_callback_function();
+}