After this change node::process_batch also works for node
implementations that do not support simd arguments for process_one.

ChangeLog:

	* graph.h (detail::wider_native_simd_size): Renamed from
	larger_native_simd_size.
	(detail::any_node): Finish concept testing for process_one
	signature.
	(detail::node_can_process_simd): New.
	(node::process_batch): Take SIMD branch only if
	Derived::process_one can be called with simd arguments.
	(merged_node::process_one(simd...)): Require that Left and Right
	process_one can be called with simd arguments.

The new node::process_batch function calls process_one for processing as
many elements as given via the input ranges. The function expects all
input ranges to be of the same size. This is encoded as a pre-condition
in the function body.

The first argument to process_batch is a buffer that provides simple
span<return_type> access. This is still an *incorrect* solution since
return_type is a std::tuple of all output port types. A correct solution
provides access to a span per type in the return_type tuple.

If all input and output ranges are contiguous ranges, and if all input
and output port types are vectorizable (in the std::experimental::simd
definition), then process_batch calls process_one with simd<T> arguments
instead of T. This is still missing a correct constraint on the
process_one function, testing whether it actually works with simd
arguments.

ChangeLog:

	* ce.cpp (test1): New function. Tests the generic process_batch
	implementation and its capabilities to use stdx::simd.
	* graph.h (detail::precondition): New.
	(port_data): New.
	(node::process_batch_simd_epilogue): New.
	(node::process_batch): New.
	(adder::process_one): Accept simd<T, Abi> or T.
	(scale::process_one): Accept simd<T, Abi> or T.
	(merged_node::process_one): Accept simd<T, Abi> or T.
	* typelist.h (meta::transform_types): New.
	(meta::transform_value_type): New.
	(meta::reduce): New.
	(typelist::construct): New.

This is the correct default because the goal of merging nodes is to
improve performance. If all intermediate results were returned (passed
on) then the optimization would be greatly reduced.

ChangeLog:

	* ce.cpp: Adjust for different return type of merged node.
	* graph.h (any_node): Move into detail namespace. Implement the
	concept, though the check for process_one does not compile yet.
	(node): Add return_type member type and make default constructor
	protected (never to be constructed directly).
	(duplicate): New node type that copies its input to `Count`
	outputs.
	(merged_node): Remove connected output port from output_ports.
	(merged_node::process_one): Move the result from the connected
	output port from apply_left into apply_right and remove it from
	the tuple returned from the function.

ChangeLog:

	* ce.cpp: New file.
	* graph.h: New file.
	* typelist.h: New file.