simplify testing and improved output
improve contributing guidelines
Merge pull request #85 from cebe/simplify-tests

simplify testing and improved output
resolve #89
resolve #88, resolve #81
reference labels should be case insensitive
resolve #82
fix reference
simplify reference
improve tests
resolve #92
Run the testsuite on PHP 5.6
Merge pull request #98 from hkdobrev/php-5.6

Run the testsuite on PHP 5.6
support HR and headings as block markups
simple html cases
Merge pull request #110 from wkpark/hr_heading

support HTML hr and headings
fixup internal reference labling to make code more readable
Merge pull request #114 from wkpark/fixup_reference_label

fixup internal reference labling to make code more readable
parser should be less dependent on compiler
remove obsolete variables