Support for input inversion

Added support for input inversion. If you have a keypad where the circuit is closed as long as no key is pressed and open while pressing a key you can now use the setInvertInput method on the ButtonMatrix to make those keypads work.

Fixed example issues & duplicate definition in ButtonBaseItf.h

• Removed namespace prefix from buttons declaration in examples
• Added preprocessor directive to avoid multiple inclusion of ButtonBaseItf.h

Minor tweaks

• Temporarily removed dbl click action (not yet implemented)
• Library name is now the same for PlatformIO as well as for Arduino IDE
• Examples: Changed pins to allow running on an Arduino Nano out of the box

First release

First release of library