Expanded to sessionStorage with a simple check.

It does not break code as it just depends on the addition of an argument
Builds, Configures Gruntfile and Simplifies the main JS.

This commit configures Gruntfile to build the minified version with the version and also date.
The lib now support also sessionStorage without breaking previous code.
Some simplifications on the code are made.
Merge pull request #3 from cirocosta/feat/expand_to_session

Expanded to sessionStorage with a simple check. Fixes #2