Value has several methods to cast value to specific type:

• Object
• Array
• String
• Number
• Boolean

Each of them checks that the value has correct type and returns a new object for the value.

For each of these methods, we should add a counterpart method IsXxx (e.g. IsObject for Object) which just checks that the value has specific type, but does not create a new object, but instead returns the original (receiver) object.

New methods should have documentation comments and unit tests.

Related: #252