Added placeholder-msg support and more documentation to jquery.localize

Added placeholder-msg support and more documentation to jquery.localize

* Added examples of all options (prefix, keys and params)
* Added example of raw attribute being used to bypass escaping
* Added documentation to code where it seemed clarification was needed
* Reduce duplication and simplified  some unnecessarily complex statements
* Added test for new placeholder-msg attribute support
* Made adding more attributes in the future easier
* Moved message wrapper function out of the localize function so we aren't defining it each time localize is used

Change-Id: I77593acf4c1b3974d502a1a8382cca9267af2d41