Allow adding a POST_TAGS subtree property for tags.

Closes #173

TAGS is a special property that maps to `* heading :tag:tag1:`.  So, we
cannot use that as a property to store our post tags.  Instead use
POST_TAGS.
Change copyright date, email.
Don't kill the org2blog-tests.org buffer on ert run.

Copy the contents of the file to a temp buffer, when trying to get
source of a particular block.
Bump up version to 0.9.1.
Use org's standard `buffer-narrowed-p'
Merge pull request #174 from gabc/master

Use org's standard `buffer-narrowed-p'
fix apparent typo in file-regexp

.?* doesn't make any sense, but it's clear we want non-greedy matching
here.
preserve any attributes in <img>

If we have:

  #+ATTR_HTML: :alt my first image :style width: 500px; display: block;
  [[file:image1.png]]

which produces:

  <img src="image1.png" alt="my first image" style="width: 500px; display: block;" />

then we must preserve the extra attributes in
org2blog/wp-upload-files-replace-urls.
Add test for preserving img attributes.

Closes #175.
Bump up version.