Use type traits and features of C++11, then use Boost.MP11.
Remove unused and unnecessary metafunctions in `detail` namespace.
Remove explicit access to ::type as no longer necessary with MP11.
Clean up and reformat code according to the current guidelines.
Legacy tests have been updated where necessary to accommodate
switch to MP11.
Replace std::is_integral with gil::detail::is_channel_integral
Replacing boost::is_integral with std::is_integral is C++ UB:
C++11 / 20.11.2 Header <type_traits> synopsis
1 The behavior of a program that adds specializations for any
of the class templates defined in this subclause is undefined
unless otherwise specified.
Implements also proposal in #93Closes#229
Document maintenance rules of `test/legacy/` content.
Motivation to move the `test/legacy/` is to:
* clarify status of those tests
* make it easier to run tests selectively
* separate new/upcoming feature-specific tests
from those all-in-one tests.
Other changes:
Rename `gil_test_common.hpp` to `unit_test.hpp` to make
it clearer it acts as `boost/test/unit_test.hpp proxy`.
Remove `<include>$(BOOST_ROOT)` from `Jamfile`-s as unnecessary.
