Added assertDoesNotThrow* assertions (and more)

[ghost]

• Added two new assertions assertDoesNotThrow and assertDoesNotThrowWithMessage.
• Updated documentation and corresponding tests.
• Now these assertions can be used with callable functions that expect parameters!
• Removed support for PHPUnit 6 version, since functionalities present since PHP 7.1 were required.
• Added phpunit.xml file.
• Test on php 7.3 and 7.4 .

Note 1: this should be tagged as version 1.1.x or 2.x to allow people using PHPUnit 6 to stay 1.0.x
Note 2: These changes would allow adding this library as a dependency in 'Verify' and eliminate this possible duplicate code.

@Naktibalda waiting for review.

[DavertMik]

Thank you! Looks good to me

[DavertMik]

I think we can tag this 1.1