fix(core): Switch back to ng-model and $watch to preview refresh purpose

The preview is now force-refreshed everytime the binded variable changes, particularly usefull when two markdown are binded on the same.
Passing the link shortcut into the compile post function for future optimization regarding the elastic directive.

BREAKING CHANGE: Instead of the `content` attribute to bind the value, you should now use the `ng-model`.

Closes #3.
refactor(core): updating revisions of the package

Since we have a major change, updating to 2.0
refactor(core): beginning of directive tests

Reformatting gulpfile, preparing tests
adding proper dependencies
test(ui): adding some tests

Tests, but need to reset the whole document to prevent duplicates of
the markdown elements.
test(core): working tests

Adding the afterEach to clean the previous generated markup, tests
passing.
[Warn] Failing test, wrong logic
[Warn] testint tests
test(core): much cleaner structure for tests, adding some

Entierely refactor the test environnement which was a little dirty,
Adding some tests, proceeding to test the editor other functionalities
test(markdown): adding some test for basic markup

Adding tests about the markup of the following components:
-code blocks
-image
-numbered list
-simple child lists
-headings
-separator
refactor(tests): moving resetContent

Moving the reset of the content inserted in the document for future implementation
of the tests that will allow to change the markup easily
Merge branch 'feature/tests' into develop
chore(travis): adding travis.yml file

Attempt to get the travis test passing
chore(travis): Build Status in Readme and launching tests
chore(travis): trying to install chrome on travis
chore(travis): Chrome not working with Travis

https://github.com/travis-ci/travis-ci/issues/938

Switching to Firefox for running the tests on Travis
fix(travis): missing firefox launcher
Merge branch 'release/2.0.0'