Default Model.raise_on_typecast_failure to false

This is probably the most changed model setting.  Almost all
web applications are not going to want to wait to save to validate
settings, they aren't going to want exceptions raised on
attribute assignment.
Move cache_anonymous_models to Sequel module

The problem with the current implementation is that it allows
calling cache_anonymous_models in a model subclass, even though
it has no effect.
No automatic class methods from dataset methods

This leads to problems.  For example, even the model plugins
loaded by default add the following class methods unintentionally:

  [:complex_expression_sql_append, :eager!, :eager_graph!,
   :insert_sql, :model, :model=]