Add exploratory test feature aborted

Run with: radish -b radish features --junit-xml=result.xml

Produces junit xml:
```
<?xml version='1.0' encoding='utf-8'?>
<testsuites time="0.000">
  <testsuite name="Test summing numbers" failures="0" errors="0" skipped="1" tests="2" time="0.000">
    <testcase classname="Test summing numbers" name="Sum two numbers" time="0.000"/>
    <testcase classname="Test summing numbers" name="Sum three numbers" time="0.000">
      <skipped/>
    </testcase>
  </testsuite>
  <testsuite name="Test summing numbers" failures="0" errors="0" skipped="2" tests="2" time="0.000">
    <testcase classname="Test summing numbers" name="Sum two numbers" time="0.000">
      <skipped/>
    </testcase>
    <testcase classname="Test summing numbers" name="Sum three numbers" time="0.000">
      <skipped/>
    </testcase>
  </testsuite>
</testsuites>
```

Author: fliiiix

tests/exploratory/abortedfeature/features/01-SumNumbers.feature

@@ -0,0 +1,18 @@
+Feature: Test summing numbers
+  In order to test the basic
+  features of radish I test
+  to sum numbers.
+
+  Scenario: Sum two numbers
+    Given I have the number 5
+      And I have the number 3
+    When I sum them
+    Then I expect the result to be 8
+
+  Scenario: Sum three numbers
+    Given I have the number 5
+      And I have the number 3
+      And I have the number 2
+    When I sum them
+    Then I expect the result to be 10
+    Then I crash

tests/exploratory/abortedfeature/features/02-NeverRuns.feature

@@ -0,0 +1,17 @@
+Feature: Test summing numbers
+  In order to test the basic
+  features of radish I test
+  to sum numbers.
+
+  Scenario: Sum two numbers
+    Given I have the number 5
+      And I have the number 3
+    When I sum them
+    Then I expect the result to be 8
+
+  Scenario: Sum three numbers
+    Given I have the number 5
+      And I have the number 3
+      And I have the number 2
+    When I sum them
+    Then I expect the result to be 10

tests/exploratory/abortedfeature/radish/steps.py

@@ -0,0 +1,24 @@
+import sys
+
+from radish import then, when
+from radish.stepregistry import step
+
+
+@step("I have the number {number:g}")
+def have_number(step, number):
+    step.context.numbers.append(int(number))
+
+
+@when("I sum them")
+def sum_numbers(step):
+    step.context.result = sum(step.context.numbers)
+
+
+@then("I expect the result to be {result:g}")
+def expect_result(step, result):
+    assert step.context.result == result
+
+
+@then("I crash")
+def crash(step):
+    sys.exit(1)

tests/exploratory/abortedfeature/radish/terrain.py

@@ -0,0 +1,6 @@
+from radish import before
+
+
+@before.each_scenario
+def init_numbers(scenario):
+    scenario.context.numbers = []