Replace global compile options and definitions with interface targets.
Remove globing for headers.
Set project version based on GIL version.
Remove GIL_BUILD_TESTS option as redundant - there is no point in
using CMake for development of header-only library if no tests
are to be built.
The assignment was superfluous in general case and incorrect in specific
case when the algorithm was given a lambda expression.
The copy assignment operator is defined as deleted for lambda
expressions.
Add minimal test for for_each_pixel algorithm to verify it compiles with
lambda expression.
