use a resource system to load images and stylesheet

resources.py

@@ -0,0 +1,17 @@
+import os.path
+import sublime
+
+def get_resource(resource):
+    path = 'Packages/MarkdownLivePreview/resources/' + resource
+    abs_path = os.path.join(sublime.packages_path(), '..', path)
+    if os.path.isfile(abs_path):
+        with open(abs_path, 'r') as fp:
+            return fp.read()
+    return sublime.load_resource(path)
+
+resources = {}
+
+def plugin_loaded():
+    resources["base64_loading_image"] = get_resource('loading.base64')
+    resources["base64_404_image"] = get_resource('404.base64')
+    resources["stylesheet"] = get_resource('stylesheet.css')