= New Features

* An exception_page plugin has been added for displaying debugging
  information for a given exception.  It is based on
  Rack::ShowExceptions, with the following differences:

  * Not a middleware, so it doesn't handle exceptions itself, and
    has no effect on the callstack unless the exception_page
    method is called.
  * Supports external javascript and stylesheets, allowing context
    toggling to work in applications that use a content security
    policy to restrict inline javascript and stylesheets (:assets,
    :css_file, and :js_file options).
  * Has fewer dependencies (does not require ostruct and erb).
  * Sets the Content-Type for the response, and returns the body
    string, but does not modify other headers or the response status.
  * Supports a configurable amount of context lines in backtraces
    (:context option).
  * Supports optional JSON formatted output, if used with the json
    plugin (:json option).

  Because this plugin just adds a method you can call, you can
  selectively choose when to display a debugging page and when not
  to, as well as customize the debugging parameters on a per-call
  basis (such as returning JSON formatted debugging information
  for JSON requests, and HTML formatted debugging information for
  normal requests).

= Other Improvements

* The common_logger plugin now correctly handles cases where an
  exception is being raised and there is no rack response to
  introspect.

= Backwards Compatibility

* Stream#write in the streaming plugin now returns the number of
  bytes written instead of self, so it works with IO.copy_stream.
