Compile-time lazy expressions and functions

Detailed Description

Generic lazy expressions and tools to manipulate them.

Lazy expressions are called lazy because they are not evaluated right away. Instead, they usually return some proxy, i.e. lazy, object which can be used to create new lazy expressions and which can be evaluated whenever the result is actually needed.

Topics
	Automatic assignment
	Automatic assignment uses lazy expressions and placeholders to simplify assigning values to multi-dimensional arrays/views and other container like objects.
	CLEF utilities
	Various internally used type traits and overloads of the operator<< to output lazy objects to a std::ostream.
	Evaluation of lazy objects
	A generic nda::clef::eval function which forwards the evaluation to specialized evaluators.
	Lazy expressions, functions and operations
	Classes that represent lazy expressions, functions and operations.
	Placeholders
	Lazy objects that can be used in lazy expressions.