Guice module - add new scenario scope

This commit adds a new Cucumber scenario scope to the Guice scopes available for use in your test code.

I realise this may be considered a controversial pull request as it's a complete rewrite of the module, rather than an incremental change. It's also not backwards compatible with the previous version of the module due to the new lifecycle of the Guice injector, see documentation below for details. 

I'd be interested to hear whether the maintainers would consider rolling this out, and if so how it could fit into the roadmap given it's a breaking change?

From the new documentation in `package.html`:

```
<body>
<p>
    This module allows you to use Google Guice dependency injection in your Cucumber tests. Guice comes as standard with
    singleton scope and 'no scope'. This module adds Cucumber scenario scope to the scopes available for use in your
    test code. The rest of this documentation assumes you have at least a basic understanding of Guice. Please refer to
    the Google documentation if necessary, see https://code.google.com/p/google-guice/wiki/Motivation?tm=6

    <b>About scopes, injectors and migration from earlier versions</b>

    It's important to realise the differences in how this module functions when compared with earlier versions. The
    changes are as follows.

    <= 1.1.5    A Guice injector is created at the start of each test scenario and is destroyed at the end of each test
                scenario. There is no scenario scope, just singleton and 'no scope'.

    > 1.1.5     A Guice injector is created once before any tests are run and is destroyed after the last test has run.
                Before each test scenario a new scenario scope is created. At the end of the test scenario the scenario
                scope is destroyed. Singleton scope exists throughout all test scenarios.

    Users wishing to migrate to this version should replace <code>@Singleton</code> annotations with
    <code>@ScenarioScope</code> annotations. Guice modules should also have their singleton bindings updated. All
    bindings in <code>Scopes.SINGLETON</code> should be replaced with bindings in <code>CucumberScopes.SCENARIO</code>.

    <b>Using the module</b>

    By including the <code>cucumber-guice</code> jar on your <code>CLASSPATH</code> your Step Definitions will be
    instantiated by Guice. There are two main modes of using the module: with scope annotations and with module
    bindings. The two modes can also be mixed. When mixing modes it is important to realise that binding a class in a
    scope in a module takes precedence if the same class is also bound using a scope annotation.

    <b>Scoping your step definitions</b>

    Usually you will want to bind your step definition classes in either scenario scope or in singleton scope. It is not
    recommended to leave your step definition classes with no scope as it means that Cucumber will instantiate a new
    instance of the class for each step within a scenario that uses that step definition.

    <b>Scenario scope</b>

    Cucumber will create exactly one instance of a class bound in scenario scope for each scenario in which it is used.
    You should use scenario scope when you want to store state during a scenario but do not want the state to interfere
    with subsequent scenarios.

    <b>Singleton scope</b>

    Cucumber will create just one instance of a class bound in singleton scope that will last for the lifetime of all
    test scenarios in the test run. You should use singleton scope if your classes are stateless. You can also use
    singleton scope when your classes contain state but with caution. You should be absolutely sure that a state change
    in one scenario could not possibly influence the success or failure of a subsequent scenario. As an example of when
    you might use a singleton, imagine you have an http client that is expensive to create. By holding a reference to
    the client in a class bound in singleton scope you can reuse the client in multiple scenarios.

    <b>Using scope annotations</b>

    This is the easy route if you're new to Guice. To bind a class in scenario scope add the
    <code>cucumber.runtime.java.guice.ScenarioScoped</code> annotation to the class definition. The class should have
    a no-args constructor or one constructor that is annotated with <code>javax.inject.Inject</code>. For example:

    <code>
        import cucumber.runtime.java.guice.ScenarioScoped;
        import javax.inject.Inject;

        @ScenarioScoped
        public class ScenarioScopedSteps {

            private final Object someInjectedDependency;

            @Inject
            public ScenarioScopedSteps(Object someInjectedDependency) {
                this.someInjectedDependency = someInjectedDependency;
            }

            ...
        }
    </code>

    To bind a class in singleton scope add the <code>javax.inject.Singleton</code> annotation to the class definition.
    One strategy for using stateless step definitions is to use providers to share stateful scenario scoped instances
    between stateless singleton step definition instances. For example:

    <code>
        import javax.inject.Inject;
        import javax.inject.Singleton;

        @Singleton
        public class MyStatelessSteps {

            private final Provider&lt;MyStatefulObject&gt; providerMyStatefulObject;

            @Inject
            public MyStatelessSteps(Provider&lt;MyStatefulObject&gt; providerMyStatefulObject) {
                this.providerMyStatefulObject = providerMyStatefulObject;
            }

            @Given("^I have (\\d+) cukes in my belly$")
            public void I_have_cukes_in_my_belly(int n) {
                providerMyStatefulObject.get().iHaveCukesInMyBelly(n);
            }

            ...
        }
    </code>

    See https://code.google.com/p/google-guice/wiki/InjectingProviders "Providers for Mixing Scopes"

    <b>Using module bindings</b>

    As an alternative to using annotations you may prefer to declare Guice bindings in a class that implements
    <code>com.google.inject.Module</code>. To do this you should create a class that implements
    <code>cucumber.runtime.java.guice.InjectorSource</code>. This gives you complete control over how you obtain a
    Guice injector and it's Guice modules. The injector must provide a binding for
    <code>cucumber.runtime.java.guice.ScenarioScope</code>. It should also provide a binding for the
    <code>cucumber.runtime.java.guice.ScenarioScoped</code> annotation if your classes are using the annotation. The
    easiest way to do this it to use <code>CucumberModules.SCENARIO</code>. For example:

    <code>
        import com.google.inject.Guice;
        import com.google.inject.Injector;
        import com.google.inject.Stage;
        import cucumber.api.guice.CucumberModules;
        import cucumber.runtime.java.guice.InjectorSource;

        public class YourInjectorSource implements InjectorSource {

            @Override
            public Injector getInjector() {
                return Guice.createInjector(Stage.PRODUCTION, CucumberModules.SCENARIO, new YourModule());
            }
        }
    </code>

    Cucumber needs to know where to find the <code>cucumber.runtime.java.guice.InjectorSource</code> that it will use.
    You should create a properties file called <code>cucumber-guice.properties</code> and place it in the root of the
    classpath. The file should contain a single property key called <code>guice.injector-source</code> with a value
    equal to the fully qualified name of the <code>cucumber.runtime.java.guice.InjectorSource</code>. For example:

    <code>
        guice.injector-source=com.company.YourInjectorSource
    </code>

</p>
</body>
```