Use the new export mechanism of Org for org2blog.

We use a custom exporter defined in ox-wp, to improve the robustness
of org2blog publishing.  Lots of clunky code is gone!

    - The LaTeX export is improved.
    - The source code blocks should be handled better.
    - Support for older versions of org is deliberately dropped.  That
      code could be moved into a legacy branch.

Issues:

  - The image/file upload looks clunky, because we still use the old
    style post-processing.  I'm not sure what's the best way to fix it

Fixes #109.
Fix post-subtree commands to use the new exporter.
Fix exports that use sourcecode shortcode

Use the correct language, and the language map, if one is defined.
Adds feature to insert table of contents

Fixes #112
Add basic framework for tests along with few simple tests.
Post full buffer instead of only visible stuff

Fixes #133
Add test for #31
Remove useless whitespace in tests.org
Add test for #125.

No fix needed on experimental branch, since it is based on new org
export framework, and is more robust!
Add test for #120.
Don't restart org-mode

Org-mode was being restarted everytime a post is being parsed, to
update any changed options in the post (see: 50a5f5ff).  This is no
longer required with the new org-mode.

Closes #135.
Change version to 0.8

Issue #101
Reorganize issues/tests in tests.org
More reorganization of tests.org
Change ox-wp to be org 8.1 compatible.

Also increment our version number.
Add one more simple test.
Add methods to post subtree as page.
Fix typo.

Trust me, I wasn't drunk!
Merge pull request #154 from RenWenshan/wenshan

Fix #134, deal with org-mode's new comment format
Add a travis.yml.