Rename some functions, improve documentation

app/doc/Class.plantuml

@@ -9,8 +9,15 @@ interface Sensor {
         {abstract} string name()
 }
 
-class HwmonFan {
+class PwmControl {
+        +void pwm(int percent)
+        +int pwm()
 
+        + void enableManualControl()
+        + void reset()
+
+        - System Paths
+        - Initial Values
 }
 
 Fan <|-- HwmonFan

app/include/fan/Fan.h

@@ -3,8 +3,8 @@
 
 class Fan {
 public:
-  virtual void PWM(int percent) = 0;
-  virtual int RPM() = 0;
+  virtual void pwm(int percent) = 0;
+  virtual int rpm() = 0;
 };
 
 #endif // FAN_H_

app/include/fan/HwmonFan.h

@@ -12,8 +12,8 @@ public:
   HwmonFan(std::unique_ptr<PwmControl> pwmControl,
            std::unique_ptr<Sensor> rpmSensor);
 
-  void PWM(int percent) override;
-  int RPM() override;
+  void pwm(int percent) override;
+  int rpm() override;
 
 private:
   std::unique_ptr<PwmControl> mPwmControl;