* Add comprehensive tests for some core classes
 * Rewrite devicetree.py to use Python functions rather than system
  * Minor bug fixes picked up through testing and linting
  * Add Travis and GitHub actions CI integration
  * Use raw strings for regexes to avoid parsing warnings on 3.8
   * Refactoring of register class to ease testings

Fixes: Xilinx/PYNQ-Dev#254