fix#1417
* New get_lowest_layer free function works for any object
* New lowest_layer_type trait works for any object
* New examples and documentation on layered streams
API Changes:
* The member function lowest_layer is removed from all
types provided by the library:
Actions Required:
* Call the free function get_lowest_layer instead of
member lowest_layer.
fix#1293
* Build ASIO's non-template entities into a static library
to reduce the compiler's memory usage during test compilation.
* Retry as single-threaded build after the first build failure.
