Add options.dumpException.  Don't re-parse coffee-script - assume we are using source maps.

## Changes in this PR:

* Don't try to read source files that don't exist when injecting source lines.
* Don't recompile coffee-script to get JS source - coffee-script now has source map support, so
  the line numbers should be coffee-script line numbers.  Also, requiring coffee-script 1.6.3 here was wiping
  out our source-map handler from coffee-script 1.7.1.  :P
* Add build script to package.json, so you can `npm run-script build` to build this.
* Make `dumpException` option functional - if false, don't dump the exception to stderr.  If a function, then pass the original exception to the function and let someone else deal with it.
* Remove "MATCH>>" debug logging.