Deprecate C ds18b20 module (#2581)

Author: nwf

app/modules/ds18b20.c

@@ -67,6 +67,9 @@ static int ds18b20_lua_readoutdone(void);
 // Setup onewire bus for DS18B20 temperature sensors
 // Lua: ds18b20.setup(OW_BUS_PIN)
 static int ds18b20_lua_setup(lua_State *L) {
+
+	platform_print_deprecation_note("ds18b20 C module superseded by Lua implementation", "soon");
+
 	// check ow bus pin value
 	if (!lua_isnumber(L, 1) || lua_isnumber(L, 1) == 0) {
 		return luaL_error(L, "wrong 1-wire pin");

docs/en/modules/ds18b20.md

@@ -3,7 +3,14 @@
 | :----- | :-------------------- | :---------- | :------ |
 | 2017-06-11 | [fetchbot](https://github.com/fetchbot) | [fetchbot](https://github.com/fetchbot) | [ds18b20.c](../../../app/modules/ds18b20.c)|
 
-This module provides access to the DS18B20 1-Wire digital thermometer. Note that NodeMCU offers both a C module (this one) and [a Lua module for this sensor](https://github.com/nodemcu/nodemcu-firmware/tree/dev/lua_modules/ds18b20). See [#2003](https://github.com/nodemcu/nodemcu-firmware/pull/2003) for a discussion on the respective merits of them.
+This module provides access to the DS18B20 1-Wire digital thermometer.
+
+## Deprecation Notice
+
+Note that NodeMCU offers both a C module (this one) and [a Lua module for this
+sensor](https://github.com/nodemcu/nodemcu-firmware/tree/dev/lua_modules/ds18b20).
+The C implementation is deprecated and will be removed soon; please transition
+to Lua code.
 
 ## ds18b20.read()
 Issues a temperature conversion of all connected sensors on the onewire bus and returns the measurment results after a conversion delay in a callback function.

lua_modules/ds18b20/README.md

@@ -1,6 +1,6 @@
 # DS18B20 Module
 
-This is a Lua module for the DS18B20 1-Wire digital thermometer. Note that NodeMCU offers both a Lua module (this one) and [a C module for this sensor](http://nodemcu.readthedocs.io/en/latest/en/modules/ds18b20/). See [#2003](https://github.com/nodemcu/nodemcu-firmware/pull/2003) for a discussion on the respective merits of them.
+This is a Lua module for the DS18B20 1-Wire digital thermometer.
 
 ## Require
 ```lua