fixed nested list parsing

fixes #49
fixed issue with | in text where no table is present
adjusted readme
added support for line breaks inside of links and references
Update README.md
refactored Markdown class to use traits

all markdown features are now in a trait so composing new markdown
flavors is as simple as adding traits to the class
started work on github markdown and markdown extra

- absy support
- traits
adjusted github markdown to use traits
final cleanup and review for default + github md
Markdown Extra
replace invalid utf8 characters

fixes #46
updated docs
Merge pull request #67 from cebe/trait-refactoring

refactored Markdown class to use traits
Update .travis.yml

allow hhvm-nightly to fail. this is currently broken somehow on travis.
added abstract methods to traits
micro optimization for indentify functions
be more GFM compatible according to lists

fixes #65
fixed endless loop bug with blockquote
removed table trait from default markdown
use composer autoloader in `bin`