Added onPersist callback and associated tests.
Added a line of documentation for onPersist showing how to use it.
Merge pull request #42 from swanjr/add_on_store_callback

Added onPersist callback and associated tests.
- force mocha-phantomjs@2.0.3 for travis
replacing attr by adequate prop
Merge branch 'gh-pages' of https://github.com/davilious/Garlic.js into gh-pages
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