Implement anchor tags
Merge pull request #22 from Barrucadu/anchors

Syntax for anchors: [[#xxx]]
Implement in-table markup.

Specifically, the following are allowed:
 - Ordered lists
 - Unordered lists
 - Code blocks
 - NoWiki blocks
 - Lines of text.
Don't break the last list item in a table
Allow table cells to contain multiple InTable nodes, and define START for table cells to be whitespace-insensitive