Support for /// <reference /> syntax to the Less editor

When building out a project using a main.less file that imports others having the ability to reference less files from the imported files is nice for completion within the editor and rendering of compiled output in the margin. The editor in Visual Studio 2013 already supports the /// <reference path="file.less" /> syntax, but the less compiler does not (and for that matter should not). 

Certain less libraries also don't support the newer @import (reference) syntax that the current version of lessc allows for, so the idea behind this work was to enable the use of the Visual Studio reference syntax and preprocess the file at compile time for rendering in the margin. Under this scenario standalone compilation of these file will not work, but with this type of less development it is also not desired since they will only be used as imports to the main file.