Add 500px and Searchcode engines

Allow to search for images on 500px. It doesn't use the official API, but the page result. Less stable, but less API key to possess...

Two engines were necessary for Searchcode because there are to search mode : search for documentation or search for code example. Both use open APIs.

searx/engines/500px.py

@@ -0,0 +1,57 @@
+## 500px (Images)
+#
+# @website     https://500px.com
+# @provide-api yes (https://developers.500px.com/)
+#
+# @using-api   no
+# @results     HTML
+# @stable      no (HTML can change)
+# @parse       url, title, thumbnail, img_src, content
+#
+# @todo        rewrite to api
+
+
+from urllib import urlencode
+from urlparse import urljoin
+from lxml import html
+
+# engine dependent config
+categories = ['images']
+paging = True
+
+# search-url
+base_url = 'https://500px.com'
+search_url = base_url+'/search?search?page={pageno}&type=photos&{query}'
+
+
+# do search-request
+def request(query, params):
+    params['url'] = search_url.format(pageno=params['pageno'],
+                                      query=urlencode({'q': query}))
+
+    return params
+
+
+# get response from search-request
+def response(resp):
+    results = []
+    
+    dom = html.fromstring(resp.text)
+    
+    # parse results
+    for result in dom.xpath('//div[@class="photo"]'):
+        link = result.xpath('.//a')[0]
+        url = urljoin(base_url, link.attrib.get('href'))
+        title = result.xpath('.//div[@class="title"]//text()')[0]
+        img_src = link.xpath('.//img')[0].attrib['src']
+        content = result.xpath('.//div[@class="info"]//text()')[0]
+
+        # append result
+        results.append({'url': url,
+                        'title': title,
+                        'img_src': img_src,
+                        'content': content,
+                        'template': 'images.html'})
+
+    # return results
+    return results