Fixed typo in docs
Using kwargs instead of hard-coded id parameter

Even though AlchemyView doesn't handle composite foreign keys this
change makes it easier to use AlchemyView together with composite keys.

Sending in kwargs instead of a specified `id` key makes it possible to
override `get`, `post`, `put`, `index` and `delete` for routes that
requires more than one parameter.
Support for custom update procedure

AlchemyView._update_item is used for updating an item.
AlchemyViewMixin class

AlchemyViewMixin class contains all code, AlchemyView just calls
protected methods on AlchemyViewMixin. This makes it easier to use
custom routes.