Add less support

**Variables**
I added a spacing variable for the 20px offset.  This way users can modify it at compile time to match their needs.

I prefixed the variables with `ngt` in both the LESS and SASS files, so we don't collide with other files loaded after ngToast.  On second thought, it seems like `toast` would be better suited.  Let me know what you think.

**Testing Generated CSS**
`grunt` now tests to ensure the generated LESS and SASS css files match.  If they do not match, then grunt will throw a warning and abort the build.  You also get a pretty view of the css differences:

![image](https://cloud.githubusercontent.com/assets/5067638/4785542/5eae674a-5d80-11e4-9c5e-14ec55d9dc05.png)

One draw back is that this is not an actual test, but a grunt task.  So, it's excluded from the travis test step.  Any ideas on how to include this?

**README.md**
I initially fixed a couple typos and added some syntax highlighting, then got a little carried away on prettifying the readme.  Let me know if you want to revert anything back to the original verbiage or layout.  Here is the rendered [updated readme](https://github.com/tameraydin/ngToast/blob/4733e4fa264c362481be205f035e9481ca60cde9/README.md).