Small cleanups

* update/remove/add comments
* delete some unused code in CommentableLines (leftover after extraction from CommentLines)
* make CommentFormatter a better object (hide its attrs, memoize its result)
Rename variables lines_and_indexes -> line_num_to_indexes
Can parse ->{} and ->.()
Fix bug where AddAnnotations added an extra newline, causing output to creep down the page
Fix bug around assignments
Remove isolation tags from specs
More hacking around recording heredocs *sigh*
Bump version to 2.0.0.beta2
Update todo in readme