Start implementation of generic pointers
Working version of generic<> pointer type
Fix Doxygen code-inline syntax

The code block was not closed and the Doxygen parser was lost in a subtle
way, showing up the TRISYCL_IMPL macro everywhere.
Hide implementation of generic<T> in SYCL API Doxygen documentation
Merge branch 'master' into future

Conflicts:
	include/CL/implementation/sycl-implementation.hpp
Move GenericImpl<> into the namespaces directly inside its include file

The issue was that Doxygen read all the files and put GenericImpl<> in the
top level namespace.

But the GenericImpl<> file was also included from inside a namespace,
making it to appear at 2 different namespace levels in the documentation.
Remove experiment around boost/operators.hpp from address spaces

Using build-in operators with conversion operators seems enough.
Move enum address_space from trisycl to sycl namespace since it is not implementation

Move also to address_spaces Doxygen module.
Generalize the concept of address space

Prepare the introduction of other types than generic<> pointers.
Replace address space explicit copy constructor by a non explicit one

This is to have generic<int *> p2 = &i; to work for now.

Also replace generic<> by a type alias for the implementation to remove a
class level.
Add implementation of priv<> pointers for OpenCL __private address space
Implement constant<>, global<> and local<> for OpenCL address spaces
Implement multi_ptr<> type to statically point to any type of address space
Merge branch 'master' into future
Implement make_multi() to create a cl::sycl::multi_ptr<>

Clean up the code also.
Implement OpenCL address space support for objects
Implement OpenCL address space for fundamental types
Factorize out AddressSpaceFundamentalImpl<> to AddressSpaceBaseImpl<>

This is to prepare a more general class factorization around address spaces.
Factorize out AddressSpacePointerImpl<> into AddressSpaceBaseImpl<>
Abstract the concept of AddressSpaceVariableImpl for pointers and fundamental types