Add NTC and resistance sensor (#560)

* Add NTC and resistance sensor

Fixes https://github.com/esphome/feature-requests/issues/248

* Fix

* Fix platformio4 moved get_project_dir

esphome/components/ntc/ntc.cpp

@@ -0,0 +1,31 @@
+#include "ntc.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace ntc {
+
+static const char *TAG = "ntc";
+
+void NTC::setup() {
+  this->sensor_->add_on_state_callback([this](float value) { this->process_(value); });
+  if (this->sensor_->has_state())
+    this->process_(this->sensor_->state);
+}
+void NTC::dump_config() { LOG_SENSOR("", "NTC Sensor", this) }
+float NTC::get_setup_priority() const { return setup_priority::DATA; }
+void NTC::process_(float value) {
+  if (isnan(value)) {
+    this->publish_state(NAN);
+    return;
+  }
+
+  float lr = logf(value);
+  float v = this->a_ + this->b_ * lr + this->c_ * lr * lr * lr;
+  float temp = 1 / v - 273.15f;
+
+  ESP_LOGD(TAG, "'%s' - Temperature: %.1f°C", this->name_.c_str(), temp);
+  this->publish_state(temp);
+}
+
+}  // namespace ntc
+}  // namespace esphome