Markitup library updated
Create jQuery global variable (django 1.6 compatibility update)
Added markdonw and markdown_safe template filters
Don't call removeMarkItUp in init (it wipes out textarea when markitup is not active)
jquery.markitup.js updated again (not it's safe to call remove() twice)
Fixed 'preview' button.

1. CSRF protection made by examples in django docs (previous version was broken)
2. Use 'markdown' template tag from django_markdown (django.contrib.markup was deleted from django 1.6)
3. Use new django.shortcuts.render signature in views.py.
Merge Alexey's commits