Add AutoCloseableSoftAssertions a version of SoftAssertions to use in try-with-resources statement to void the need to call assertAll(). (Fixes #235)
Add assertThat(new ExceptionalRunnable {...}).toThrow(Exception.class) API
ExceptionalRunnableAssert: Return AbstractThrowableAssert from toThrow() method
ExceptionalRunnableAssert: Renamed assertThat() method to expect()

... to prevent overloading issues and make the needed lambda expression shorter
ExceptionalRunnableAssert: Throw AssertionError if wrong exception is thrown
ExceptionRunnable: Renamed to ThrowingRunnable

... and throw Throwable instead of Exception
Assertions: Replaced expect() method with assertThatExceptionThrownBy()
ThrowingRunnableAssert: Do not catch AssertionErrors unintentionally
ThrowingRunnableAssertTest: Check if AssertionError messages are correct