Middleware for LESS CSS

[hellogerard]

The middleware will compile LESS files on-the-fly using the Assetic library. It supports minification and caching, also via Assetic. I've been using this in my project for a couple weeks. Inspired by less-middleware from the node world.

[silentworks]

This is a great middleware. Could you create a separate repo for it and we will link it somewhere in the documentation about it or on the Slim website.

Currently adding the extra dependency to the composer.json for assetic and cssmin would be too much for some users who wouldn't make use of this middleware.

We will be changing how middleware gets added soon, maybe we will have something like the npm directory just for middleware to allow users to search for middleware available via composer (through packagist).

[hellogerard]

Done! https://github.com/hellogerard/less-slim-middleware

I guess you can close this PR...?