Explicit the ConanFile python class

Right now the `ConanFile` class is pretty much a second-class citizen in the documentation. It's all for `conanfile.py`. The problem with this approach is that you end up with stuff like this:
http://docs.conan.io/en/latest/reference/conanfile/methods.html#package

That's the documentation of the `package` method, yet it documents the `copy` method. It took me several minutes to be able to find that page. Even from the menu, even using your conventions of using parethesis after a method name, there is no reference to the `copy` method, only to `conan copy` or example calls of `self.copy`.

The grouping is also weird as the generators are out of the `conanfile.py` section, yet they may be used there. For me the `conanfile.py` documentation should just have links to the other sections of what can possibly be included in a `conanfile.py`. The documentation for the classes and methods of `ConanFile` should be really named `ConanFile`, and its methods and attributes should have a specific entry, even if they're only there for consumption and not to be overriden.

Start with the linked package-methods page and the current conanfile.py documentation, then map where ConanFile methods, attributes, and generators are currently documented. Done means ConanFile has a distinct documentation section with specific entries, while conanfile.py links to the relevant sections instead of serving as their only grouping.

Written by the indexing model from the issue text.