New Feature: to have ability to ignore all assert when expected value is null

#### Summary
to have ability to ignore all assert when expected value is null.

#### Example
Let's call the new method "ignoreAssertWhenExpectedIsNull"

```java
assertThat("Hello World!").ignoreAssertWhenExpectedIsNull().isEqualTo(null); // will pass
```

#### Further more
If go further, we could have a method as ignoreAssertWhen(IgnoreType ignoreType)

Above would be

```java
assertThat("Hello World!").ignoreAssertWhen(IgnoreType.ExpectedIsNull).isEqualTo(null); // will pass
```
IgnoreType could contains

- ExpectedIsNull
- ActualIsNull
- EitherIsNull