Several changes and bug fixes, including:

• Breaking change: coveo::enumerable now supports returning non-const references. This means that a coveo::enumerable<int> returns references to non-const ints. To return references to const objects, use something like coveo::enumerable<const int>.
• Optimized skip() and take(), including support for fast_size when possible.
• Breaking change: several operators now return values instead of references to avoid dangling references. This includes min(), max(), first(), etc.