Add amd, node and browser modularity

[gpmcadamold]

Makes the plugin modular and adds basic AMD/NodeJS compatibility. You may wish to expand on this further with patterns available at https://github.com/umdjs/umd

[juanbrujo]

Wow, I was about to do this past week, I'll test this and fill test.js (it is there empty for that purpose!) and add CommonJS aswell.

gr8 contribution!

[juanbrujo]

@gpmcadam I couldn't require as a module from your changes, maybe was needed some testing (test.js). Here's a branch where I'm working on nodejs/commonjs/amd support: https://github.com/juanbrujo/limitCharacts/tree/amd/commonjs

Maybe you can look through, it is working (run node test.js) but I'm still working in the array support.