stacks & encode

reworked stack trace extraction
- works with multi-line messages like chai-json-schem
- cut voodoo cargo-cult code

dropped excessive jsenc
- allow many utf chars
- first try JSON-style string escaping
- use jsenc only to augment JSON's escape
- centralized string escaping

error message trimmed to one line in first report
added chai-json-schema devDependency
support for Q long stacktraces 'From previous event:' and other stack decoration lines
added Q node_modules and 'node.js' file to stackfilter
cleaned up code