Adds feature for specifying --format xml

Signed-off-by: M. Scott Ford <[email protected]>

Author: mscottford

features/xml_format.feature

@@ -0,0 +1,11 @@
+Feature: Creating BOM using XML format
+
+  Scenario: Running against simple fixture
+    Given I use a fixture named "simple"
+    And I run `cyclonedx-ruby --path . --format xml`
+    Then the output should contain:
+    """
+    5 gems were written to BOM located at ./bom.xml
+    """
+    And a file named "bom.xml" should exist
+    And the generated XML BOM file "bom.xml" matches "bom.xml.expected"