Fixing command to checkout the right CakePHP version on Travis.

Travis output says:
error: pathspec '2.2.7' did not match any file(s) known to git.
The command "git checkout $CAKE_VERSION" failed and exited with 1 during before_script.

That's because when cloning with '--depth 1' it doesn't retrieves branches/tags references (on git 1.8.1 and newer).
Merge pull request #31 from renansaddam/bugfix/travisGitCheckout

Fixing command to checkout the right CakePHP version on Travis.
Adding the possiblity to define engine options.

That way we can set any options the engine may have, or override any hardcoded/default options.
i.e: http://madalgo.au.dk/~jakobt/wkhtmltoxdoc/wkhtmltopdf-0.9.9-doc.html
Creating a mocked binary of wkhtmltopdf to run on Travis.
Merge pull request #32 from renansaddam/feature/WkHtmlToPdfOptions

Adding the possiblity to define engine options.