Document the use of Thin in the README

In `sinatra_skeleton` we use naive Rack to launch
the web server.  Students might forget or be
mistaken in thinking that **this** starter pack
should be launched in the same way.

Ensure that we document the assumption that they
use Thin to run the server.
Implement a "em" helper for reference; improve README

There were some deails about the helpers
definitions that could trip beginners up e.g:

1.  Helpers are only read once
1.  They require server restart to be seen
1.  Changes are not dynamically re-incorporated
1.  etc.

Document these expectations *and also* actually
use a helper `em()` so that students can
understand how they connect to templates.
Convert helpers/README to Markdown

Get students used to seeing the most popular
richer-text syntax.
Correct misusue of e.g.
Convert models/README to Markdown
Relocate misplaced comma set
Add Demo class, spec

Provide the baseline kit an example for writing a
primitive-level spec which tests a
non-ActiveRecord class.

1.  Demonstrate that we can test classes that are
not AR.  This should provide some vaccination
against the unfortunate habit of RAils programmers
NEVER creating non-AR based `app/model`s.  Failing
to do so tends to create very non-OO code.
1.  Demonstrate the power of "helper" classes
1.  Provide a quick reference of how to write a
spec for those coming from JUnit or MiniTest
backgrounds.
Update CHANGELONG
Demo: Update implementation to work with Sinatra::Application

I wrote my implementation originally using a stub
object until I could see what the default context
passed to `Demo.new()` was.  Having tested it out
I found some non-contrived methods that
communicate what's worth testing a bit better.
Merge pull request #2 from fox-squirrels-2013/2014-01-update

2014 01 update