Add table tags to the whitelist.

Fixing:
https://github.com/russross/blackfriday/commit/55cd82008e9b35b9a03a80e06d5a4c4601320211

This commit introduced a html tag whitelist which does not include any table tags (<td>,<tr>,<thead>...). Therefore even tables the markdown parser itself generated will be removed.
tagWhitelist allows alignment attribute now

This is the closest I could get to removing everything "unsave" without introducing an additional regex.
Merge pull request #64 from willnix/master

Add table tags to the whitelist.