Convert image by domain 2.1

Convert image by domain v2.1 changes:

Attachment tables xf_attachment and xf_attachment_data are now updated more accurately to reflect original post date and post user id.

Convert image by domain v2.0 changes:

Fixed issue when multiple IMG tags were on the same line.

Convert image by domain v1.9 changes:

Now supports $config['http']['proxy'] function.

Convert image by domain v1.8 changes:

Now retains IMG bbcode options.

Convert image by domain v1.7 changes:

Added Post ID start and Post ID end to options page.

Convert image by domain v1.6 changes:

Improved PHP code relating to the search index.

Convert image by domain v1.5 changes:

Added Referer to options page. This allows converting low resolution photobucket hot linked images to high resolution attachments.

Convert image by domain v1.4 changes:

Code refactoring update.

Convert image by domain v1.3 changes:

No longer requires a specific image handler. File system operations now using XenForo file functions.

Convert image by domain v1.2 changes:

Fixed issue with undefined variable in previous version.