Ptest

- Add documentation for ptest: https://github.com/KarlGong/ptest/wiki/documentation

- Add "assert_that" assertion.

- Ignore the test group if no group features are used.

- Support run_group for TestClass.

- Support expected_exceptions for Test.

- Add command option -m(--merge-xunit-xmls) to merge the xunit result xmls.

- Add detailed information for screenshot.

- The instance variables defined in BeforeSuite, BeforeClass, BeforeGroup can be accessed by other test fixtures.

- Support custom args in test fixtures.

- Add option (--python-paths) to specify additional python paths.

- Support BeforeSuite, BeforeClass, BeforeGroup, AfterSuite, AfterClass, AfterGroup.

- Support timeout for test fixtures.

- Redesign the html report.

- Add cmd line entry points for py3.

- All temp data will be stored in temp folder.