Add SmartyPants test for trailing single quotes (see vmg/redcarpet#340)

examples:
- the students' chairs
- tryin' to fix this bug
Fix vmg/redcarpet#340 by replacing trailing single quotes
Add changelog entry for trailing single quotes (vmg/redcarpet#373)
Move changelog entry to the top of the file
use SVG to display Travis CI build testing status
Merge pull request #376 from Mithgol/patch-1

use SVG to display Travis CI build testing status [ci skip]
Merge pull request #373 from kevin1/trailing_single_quotes

Convert trailing single quotes to curly quotes
Remove trailing whitespaces
Update test_references_with_tabs_after_colon
Fix emphasis escape sequence detection

Fixes issues #214 and #369
Add changelog entry
Add = highlight character to escape_chars list
Merge pull request #380 from jcheatham/fix_214_and_369

Fix emphasis escape sequence detection
Define a Redcarpet::TestCase class

Let's have an entry point for our test suite to add eventual helpers or
define custom stuff instead of relying on Test::Unit::TestCase directly.
Avoid defining the html_equal helper at the top level

Since we now have a Redcarpet::TestCase class, let's push any helper
here and avoid defining top level methods.
Rely on #scan instead of #split

Let's rely on #scan in combination with #length instead of #split to
make the assertion more clear. Previously, we were asserting that the
array returned by #split have a length of n+1 where n is the actual
number of elements. With #scan, this is now a lot more easy to read.
Update the Gemfile for Rubinius

Rubinius doesn't require us to have rubysl or racc in our Gemfile so
let's remove them for now.
Merge pull request #382 from vmg/travis-rbx

Update the Gemfile for Rubinius
Merge pull request #381 from vmg/test-suite

Tiny improvements to the test suite
Add the escape_html option the README file [ci skip]

This option has been added in vmg/sundown#85 but has never been
documented while its behavior can be more or less unexpected.