Add info about use of colons with keywords (Closes #284)

[mlvandijk]

From #284:

** Use of colons **
From gitter: Jeff Johnson @jeffcjohnson Jan 16 20:45
When writing features, if a newbie like me puts a colon after Given, When or Then, it doesn't complain but doesn't do anything either. It took a while to figure out why my test was being ignored.
It would be helpful to clarify somewhere in the docs, possibly the Gherkin page.

Added this to the docs.

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[olleolleolle]

Good addition!

[mlvandijk]

Thanks as always @olleolleolle

[luke-hill]

I think you've potentially raised quite an interesting bug. Because to my knowledge, keywords that shouldn't have a colon such as Given should raise parser errors?

cc/ @gasparnagy something to consider? If not universally done?

[gasparnagy]

@luke-hill As the Gherkin keywords contain the space as well (e.g. Given ), if you use colons (Given:) it will not be recognized as a keyword as it does not contain the space. And because the line will start without a keyword in front, the parser will think that this is part of the scenario description and this is why these are "just ignored". The real solution for that would be to remove the space from the keywords (but it is not that easy, because some French keywords don't have the space...). Without I cannot think of an easy way to fix that.

[gasparnagy]

@mlvandijk In the Formulation book we categorized the keywords to block keywords and step keywords, using that categorization it is easier to document whether you need a colon after or not (you need it for block keywords, but not for step keywords).

[mlvandijk]

Thanks for clarifying that @gasparnagy - that might be a good addition as well