Optionally disable injection of piwik script

[tbtz]

Added an option to disable the injection of the piwik.js script into DOM.
Also added tests for the option.
Default: Injection enabled.

CAUSES:

We need to load the script separately to:

• prevent uncontrollable side effects
• prevent multiple loading if script already exists
• make loading of the script configurable

[coveralls]

Coverage remained the same at 100.0% when pulling c9daab1 on tbtz:optional-piwik-injection into 2510ae2 on joernroeder:master.

[joernroeder]

thanks for submitting your idea, code and tests 👍. Would you mind adding the option to the documentation as well. I'll merge it into master afterwards.

[coveralls]

Coverage remained the same at 100.0% when pulling cf26eec on tbtz:optional-piwik-injection into 2510ae2 on joernroeder:master.

[tbtz]

Added the option to the documentation 😊👍

[joernroeder]

thanks for your contribution. i've pushed a new 0.8.2 version to npm.