moved text, rendered_text, get_oembed_markup, render, and save to abstract
Merge pull request #16 from HN23/issue10

moved text, rendered_text, get_oembed_markup, render, and save to abstra...
Merge pull request #17 from HN23/issue-6

made changes to shorten code, added get_for_user to PostQuerySet.
Merge branch 'issue-6'