More tests for atx headings

Headings with the atx style support closing.
I have added more tests for all heading sizes, closing and closing different number of #s.
Merge pull request #7 from hkdobrev/atx-headings-tests

More tests for atx headings
paragraph blocks preceded by a list block should not produce exceptions
rename tests/ to data/
migrate tests to phpunit
improve indentation in phpunit.xml.dist
fix test case
refactor test case
Fixed performance check for quick blocks and lines
Merge pull request #11 from hkdobrev/fix-quick-block-check

Fixed performance check for quick blocks and lines
add .travis.yml config
Better parsing of emphasis and strong elements

 - Regex is based on original Perl regex.
 - Added more tests.
implement coveralls.io integration
add .coveralls.yml config
fix .coveralls.yml
add "Coverage Status" badge to readme
Merge pull request #10 from hkdobrev/emphasis

Better parsing of emphasis and strong elements
improve readme
remove link from the h2 heading in readme
remove footer from readme