Implement hooks

[raniejade]

This can be done per spec basis.

class SomeSpec: KSpec() {
    override fun configure(configuration: KSpecConfiguration) {
    }

    ...
}

Provide the following methods:

• before(example) - invoked before an example is executed.
• after(example) - invoked after an example is executed.
• around(example) - provide a way to wrap an execution of an example (e.g. run in a different thread - timeout?)