Hack to get columns evenly spaced
* #549
Replace th with td due bug at pandoc
Add style for simulate header at table
Change some anchors to enable EPUB post processor
Update gloss.md with the changes on anchors
Add post-processor at EPUB building stack

When converting HTML to EPUB using pandoc we lose the anchors
at glossary. This PR add a post-processor to restore this
anchors.

This close #550.