Ptest

- Add examples folder.

- Support declare additional arguments in test methods.

- Support py3.

- No extra package is needed to capture screenshot.

- Support default value for config.get_property().

- Add filter for test case status in html report.

- Support multiple test listeners.

- Support run/debug in Pycharm via a ptest plugin.

- Support filter test cases by group.

- No extra codes are needed to support capturing screenshot for selenium test.

- Add always_run attribute to Test.

- Add command option --disable-screenshot to disable taking screenshot for failed test fixture.

- Support group in test class.