Open current markdown file in a new window

It works for saved and unsaved files. Maybe unsaved file's content
should be written to a temporary file in case we crash, so that the user
doesn't lose all it's content.

utils.py

@@ -0,0 +1,4 @@
+import sublime
+
+def get_settings():
+    return sublime.get_settings("MarkdownLivePreview.sublime-settings")