Delete old spec assets when running tasks/parse
New heuristics for generating clauses on disk

Do a bottom-up walk of the spec's clauses. If a clause's contents,
including its subclauses' contents, is longer than 30000
(unformatted), its subclauses are imported rather than inlined.
Updated spec files from new parse implementation
Merge branch 'new-heuristic'
Write script includes to index.html in tasks/parse.js