Minor fix to Wordpress image processor.

[nyaalex]

Heya! I was trying to use this on a blog I wanted to download before a long train ride, and I noticed none of the images were being formatted properly. I noticed a few issues:

• In get_single_images() the blog2epubimage tag was prepended to the existing <img> tag, leaving it there even after processing.
  • It also did not insert a comment, so the find/replace never matched the tag.
• In get_images_with_captions() the inserted tag did not end with a # so the find/replace never matched the tag.
• The final output took from article.content whereas replace_images() only ever affected article.html

Hopefully the changes I've made make sense, they should address all of the above issues and I was able to compile a functional epub using these edits, just in time for my train too.

Thank you very much for this project, I've used it a fair few times and find it very useful. Hope you find my little contribution helpful :grin:.

[bohdanbobrowski]

Merged. Thanks @nyaalex for that!