lessphp support

a lessphp port to minify, i've taken somebody else's work and rebased it to current master

overall expression: a group with single .less file: worked

@mrclay: could you drop your guidelines how to improve and make this work as you would intend?

tasks:
- [ ] lessphp support
- [ ] support import statements (multiple file caching/monitoring)
Looks like the only difference is in constructor:

```php
 case 'less' : $this->contentType = 'text/less';
                   break;
```