CoffeeScript step definition snippets

Here's a way to get the step definition snippets in CoffeeScript syntax (raised in [issue #65](https://github.com/cucumber/cucumber-js/issues/65)). I really wanted to use them, so thought I'd go ahead and try to patch.

I've removed the static properties from `Cucumber.SupportCode.StepDefinitionSnippetBuilder ` and created new syntax behaviors `Cucumber.SupportCode.StepDefinitionSnippetBuilderSyntax.JavaScript` and `Cucumber.SupportCode.StepDefinitionSnippetBuilderSyntax.CoffeeScript` which will switch dependent on the `--coffee` CLI option.

To be honest, it's the first time I've used Jasmine properly, so you may think that what I've done could be improved.

Ta,
John