introduce jgiven-kotlin

[jangalinski]

Kotlin is working just fine with jgiven, but in day to day usage, some problems occur. This module provides useful fixes and extensions:

• it contains a JGivenStage annotation that can be used to configure the kotlin "all-open" plugin, otherwise stage classes and all stage methods would have to be explicitly marked as open
• "when" is a keyword in kotlin, so Stage.when() has to be written as Stage.'when'() ... I introduced extension properties for given()/when()/then()/... so a kotlin test can be written like:

class JGivenKotlinExtensionTest : ScenarioTest<JGivenKotlinGiven, JGivenKotlinWhen, JGivenKotlinThen>() {

  @Test
  fun `add two numbers`() {
    GIVEN
        .number(5)

    WHEN
        .we_add_number(7)

    THEN
        .the_result_is(12)
  }
}

What do you think?

Attention: this is just a kick-off PR, if you would integrate this into jgiven, we'd have to set up the dokka plugin for java doc generation.

[jangalinski]

@janschaefer did you have a chance to have a look into this?

[janschaefer]

As far as I can evaluate it (I am not a Kotlin developer) it looks good. I am not a big fan of all uppercase GIVEN, WHEN, THEN, but I guess lower case is not possible and it is just my taste.

[jangalinski]

Hi, what is the state of this PR? Any chance to consider support for kotlin for 1.0.0?