fixed [Issue 78845090] (https://www.pivotaltracker.com/story/show/78845090) ("show html" button not working)
- extracted `h(@code.tpl)` into application helper as new method `escape_markup(markup)`
- created directory test/unit/helpers to house helper tests
- added file application_helper_test.rb to house tests of application_helper
- added test of escaped markup
- fixed text_sandbox.html.erb so that test passes
Trivial to minor refactoring of sandbox view
- DRY one div
- one change to Rails 3 syntax
- change Sandbox output border color (partly white border was partly invisible in BlackOnWhite color scheme)
- move lots of styling out of view and into stylesheet (to make view logic and basics more readable; also dreaming of (in the distant future) different styling for mobile devices)
Generalized helper method to let the caller decide which (if any!) Textilization to use
- (per suggestion of @pellaea
Merge pull request #7 from JoeCohen/sandbox

Joe fixed the "show html" button in textile sandbox. (thanks!)