Bump version to 3.48.0
Remove sequel_core.rb and sequel_model.rb files
Remove the deprecated core extensions, and ruby 1.8-specific Symbol extensions from the core_extensions
Remove Deprecation.deprecated_module

This was only used for the deprecated core extensions, and I don't
think it will be used again.  The rest of Deprecation will continue
to be a part of Sequel.
Remove the identity_map plugin
Remove the pg_auto_parameterize and pg_statement_cache extensions
Don't load all extensions just to run a single extension spec

This moves the requiring of most extensions out of the spec helper,
and has the individual spec files require what they need.  To
ensure there aren't dependencies on load order, the order of
the extension specs is now randomized.
Remove SQL::SQLArray class and SQL::NoBooleanInputMethods module
Use a connection queue instead of stack by default for threaded connection pools

The :connection_handling=>:stack option can be used to get the
previous behavior.
Default to deep qualification when joining

You can override default_join_table_qualification or use the
:qualify=>:symbol option to get the previous behavior of only
qualifying symbols.
Make filter methods operate on WHERE clause even with existing HAVING clause

Make and, or, and invert work without an existing filter.
Make select_more an alias for select_append
Make from and select not treat hashes as alias specifications
Remove Dataset methods moved to sequel_3_dataset_methods
Automatically alias single expressions in Dataset#get, #select_map, and #select_order_map, to work around possible DoS issues

This removes a possible denial of service attack on databases that use
aliases that vary per input expression.  This was already warned
against in the security guide, so go ahead and delete that warning.
Remove Sequel::NotImplemented exception

Additionally, remove the deprecated default implementations that just
raised NotImplemented.  The best way to checking if something is
implemented is to use respond_to? (or a separate method to check for
support if available).
Sequel::Dataset only accepts database, Database.dataset now accepts no options
Remove Database#transaction :disconnect=>:retry option
Remove default graph_each, and each calling graph_each

Make the graph_each plugin handle this.  Since each no longer
calls graph_each, make the model associations code override each
for the eager graph checking.  This is only a temporary situation,
as eager_graph in the future will call naked on the dataset so that
each does not need to be overridden.
Require graph or set_graph_aliases precede add_graph_aliases