JC Button Versions Save

Incorporate PR #39: Change several member functions to const & add some initial values. This avoids some warnings generated by cppcheck.

Change architectures to "*" in library.properties.

Add JC_Button to keywords file so that syntax highlighting works on #include statement.

Fixes issue with UpDown.ino example.

Added ToggleButton as a derived class. Updated documentation. Added example sketch.

Bugfix: Fix constructor initializer list order.

Overview

This is a major release that is not backwards-compatible with previous releases. However, the incompatibilities are few and fairly straightforward:

1. The order of the parameters for the constructor has changed. Default values are now supplied for three of the four parameters. This simplifies coding for the most common use case, i.e. a button wired from a GPIO pin to ground and the internal AVR pullup resistor enabled. For this case, only the pin number needs to be passed to the constructor.
2. Hardware initialization (i.e. pin configuration) was moved from the constructor to a new begin() function. Therefore begin() needs to be called for each button object in setup() or other initialization code.

Other changes in this release

1. Library code and example sketches were updated for clarity, coding style and documentation.
2. Changed license to GNU GPL 3.0.

Changed the name of the library and repository from Button to JC_Button.