Naïve first attempt at implementing token-stream based rendering

* No support for strings or regexes
* No support for anonymous function shorthand
* No support for special layout for core macros
Cleanup: remove debug code from class-name helper fn
Quickfix: don't add extra spacer at start of already-indented line
Quickfix: don't add blank lines before nested multiline forms
Quickfix: collapse sequences of closing delimiters onto a single line
Markup seq heads with .head CSS class
Quickfix: ensure annotate-head doesn't choke on empty seqs
Merge branch 'master' into token-stream
Restore coloring of collection delimiters
Quickfix: don't insert extra spacers in single-line nested forms
Restore rendering support for stringlike forms
Render ::before and ::after markers for regexes
Restore seq layout extensibility