Add PWM demo code. We use libsoc for handling PWM.
Preliminary commit with the following projects in Eclipse 1. gtkmm Hello World 2. PCF8574 I2C GPIO Expander 3. PCF8591 I2C A-D & D-A Converter 4. SPI based OLED Display with SSD1306 controller Library Dependencies 1. Gtk 2. Gtkmm 3. libsoc TODO: Documentation and cleanup