Ruby 2.1.6 is latest in 2.1 line.

Ruby 2.2.2 is latest in 2.2 line.

Relates to #598

Accommodate Sass syntax tree change.

Related to #595

For now we'll need to live with old-style RSpec syntax.

Refactored the guide filename and path detection a bit -
now also keeping a separate :dir field to reference the directory.
Using "url" field for that purpose seems awkward, so replaced
all these usages with :dir.

Fixes #584

Fixes #577

Specify sass version.

Because sass 3.3.x breaks some of the css related specs of jsduck.

Although the build on ruby 1.8.7 is still failing, this change fixes the builds on ruby 1.9.3 and 2.0.0 on Travis-ci.

Refs #536

A patch by Patrick Gleichmann.

Specs by me.

Refs #527

Fixes #515

Instead of relying on offset values, align the top-right of the menu
with bottom-right of the Docs app title.

Fixes #516

For IE8+ and other browsers the ExtJS 4 framework supplies a data-uri,
but for IE 6 and 7 it defaults to an URL pointing to sencha.com,
which will cause problems when offline.

Refs #511

Only do it for the generated TOC, but leave the original HTML alone.

Fixes #507

Implement a special '@browser' keyword, which when used as:

    --external=@browser

will include all the standard browser web API classes, listing
of which taken from:

https://developer.mozilla.org/en-US/docs/Web/API

Fixes #502

Instead of :external_classes, use :external - like the name of
the option itself, and like it is now with all other options.

Quite a hack... something better is surely needed.

Allows one to supply a list of unknown tag names on which the
warning is not shown.

Fixes #500

Change the #warn method so it can be used for also passing in
arguments, and then use it for reporting the :nodoc warning too.
For this to work:

- Logger#warn expects a `file` parameter instead of `filename` and
  `linenr`, which must always be a hash.
- The fourth parameter is then free to be used as optional `args`
  array for the warning types that need it.

The support for the deprecated old format was removed a while ago,
but the warning type was forgotten to be removed, so it hanged along
without having any actual effect.

JSDuck is really only meant for documenting JS and SCSS files.

Fixes #474