feat(pwm): update pwm lib for release/v2.xx

1. Add API to stop PWM.
    2. Add API to set the phase of each PWM channel.
    3. Add pwm example.

examples/pwm_test/include/user_config.h

@@ -0,0 +1,29 @@
+/*
+ * ESPRESSIF MIT License
+ *
+ * Copyright (c) 2015 <ESPRESSIF SYSTEMS (SHANGHAI) PTE LTD>
+ *
+ * Permission is hereby granted for use on ESPRESSIF SYSTEMS ESP8266 only, in which case,
+ * it is free of charge, to any person obtaining a copy of this software and associated
+ * documentation files (the "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the Software is furnished
+ * to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all copies or
+ * substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+ * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#ifndef __USER_CONFIG_H__
+#define __USER_CONFIG_H__
+
+#endif
+