Support other plugins using the @apiExample element

[Arxcis]

Stricter pattern matching

Previously this plugin would catch all elements with the pattern:

@apiExample .*

This PR makes sure that apidoc-plugin-example only runs if the element matches any of these 3 patterns

@apiExample {json=.*
@apiExample {jsonschema=.*
@apiExample {xml=.*

Full regex here
/^\s*\{(json|jsonschema|xml)\s*=(.+?)\}\s*(?:\s+(.+?))?\s(.+?)$/g;

Bugfix

PR fixes a bug mentioned in #4, which happened because the plugin did not check if regex-match returned null before running .pop() and .push(). As an example, this would crash the apidoc command if apiExample {curl} was used together with plugin.

Further with the stricter pattern-matching mentioned above, we can remove an if-statement because we can trust parsed values more.

function parserExampleElements(elements, element, block, filename) {

  if ( element.name !== 'apiexample' ) {
    return elements;
  }

  const values = elementParser.parse(element.content, element.source);
  if (!values) {
    return elements
  }

  const data = fs.readFileSync(path.join(path.dirname(filename), values.path), 'utf8').toString();

  element = schemas[values.schema](data, values.element, values.title);
  elements.pop()
  elements.push(element);

  return elements;
}

Also we now make sure to run .pop() and .push() right next to each other, as the program will be in an inconsistent state if only one of them runs.