feat(components): add RadioButtonGroup

Closes #25

src/components/RadioButtonGroup/RadioButtonGroup.stories.js

@@ -0,0 +1,40 @@
+import { withKnobs, text, select, boolean } from '@storybook/addon-knobs';
+import Component from './RadioButtonGroup.Story.svelte';
+
+export default { title: 'RadioButtonGroup', decorators: [withKnobs] };
+
+const values = {
+  standard: 'standard',
+  'default-selected': 'default-selected',
+  disabled: 'disabled'
+};
+
+const orientations = {
+  'Horizontal (horizontal)': 'horizontal',
+  'Vertical (vertical)': 'vertical'
+};
+
+const labelPositions = {
+  'Left (left)': 'left',
+  'Right (right)': 'right'
+};
+
+export const Default = () => ({
+  Component,
+  props: {
+    group: {
+      name: text('The form control name (name in <RadioButtonGroup>)', 'radio-button-group'),
+      valueSelected: select(
+        'Value of the selected button (valueSelected in <RadioButtonGroup>)',
+        values,
+        'default-selected'
+      ),
+      orientation: select('Radio button orientation (orientation)', orientations, 'horizontal'),
+      labelPosition: select('Label position (labelPosition)', labelPositions, 'right')
+    },
+    radio: {
+      disabled: boolean('Disabled (disabled in <RadioButton>)', false),
+      labelText: text('Label text (labelText in <RadioButton>)', 'Radio button label')
+    }
+  }
+});