Refactor GPIO Monitor class

Refactor the GPIO Monitor class to use a common class, Evdev,
to inherit from. Evdev does the basic libevdev handling.

Change-Id: I427aa9720b0bbbea0284c0babcc03ece92e55f5e
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/evdev.hpp b/evdev.hpp
index b3189f1..353c593 100644
--- a/evdev.hpp
+++ b/evdev.hpp
@@ -70,8 +70,7 @@
          *  @param[in] path      - Device path to read for GPIO pin state
          *  @param[in] key       - GPIO key to monitor
          *  @param[in] event     - sd_event handler
-         *  @param[in] handler   - IO callback handler. Defaults to one in this
-         *                        class
+         *  @param[in] handler   - IO callback handler.
          *  @param[in] useEvDev  - Whether to use EvDev to retrieve events
          */
         Evdev(const std::string& path,