Update less to 1.5.1

Hi

I'm preparing to make use of lessc and figured I'd send you some pull requests after making the changes that I wanted.

This one is just a clean install of less 1.5.1 (not an update) using npm 1.3.17.

No need to actually merge, but I hope you'll update the nuget package in the near future!
I love the simplicity of the package.