added void_t (incl. voider-hack for gcc), and template aliases real_t and field_t for convenient access of T::real_type, T::field_type

Start hello world program in new projects with editor hints

Add editor hints from
https://www.dune-project.org/doc/devel/codingstyle.html in hello world
program created by duneproject.

See merge request !18

Feature/remove mpi deprecation warnings

Suppress some warnings due to deprecated methods in MPI. 

There are some warnings left due to MPI_LB and MPI_UB but I am not sure how to fix them. See http://www.mpi-forum.org/docs/mpi-2.2/mpi22-report/node76.htm.

See flyspray/FS#1610

See merge request !14

We require MPI 2.1 anyway and nobody has reported problems.

Feature/conceptcheck

This introduces the function

    template<class C, class... T>
    static constexpr bool models();

Its result indicates if the concept C is modelled by the collection
T... of types. A concept is a list of expressions that a type must
support. Concepts can refine other concepts to inherit all requirements
from those base concepts. Besides the concept check function itself, this contains
some helper functions of the form `require*` that transform
a non-matching condition to a substitution failure. E.g.,

    requireConvertible<R>(t.f())

is not valid unless the result of `t.f()` is convertible to R.

Since `models()` is the user interface, it's contained in the
namespace Dune::. In contrast the various `require*()` functions
needed for concept definitions are in the namespace Dune::Concept::.
I strongly propose that concept definitions themselves also go into
namespaces Dune::(NonCoreModule::)Concept.

This merge request depends on the TypeList feature (!7).


See merge request !9

flyspray/FS#1147: Compute norm of vectors with NaN entries properly

This is an attempt to solve the issue outlined in flyspray/FS#1147. I've yet to fix `DenseMatrix::infinity_norm` the same way.

See merge request !15

Test complex<T> for floating point T only

The standard leaves (the effect of instantiating) complex<T> for more
general T unspecified.

While we're at it, kill duplicate tests and add long double to the list.

This fixes bug flyspray/FS#1726: Now also with clang 3.7 and libstdc++ 4.9.2 on Debian 8.2, the test fvectortest can be compiled again.

See merge request !11

We require MPI 2.1 anyway and nobody has reported problems.

[cmake] fix capitalization of some SuiteSparse_ variables

There were still some variables with the old capitalization SUITESPARSE_
that prevented my own code from finding umfpack.h.

After this small fix, the code from merge request !8 works for me as expected.

See merge request !13

There were still some variables with the old capitalization SUITESPARSE_
that prevented my own code from finding umfpack.h.

Feature/typelist

This adds `template<class...T> struct TypeList {};`
together with some utilities. It's e.g. used in the
concept checking facility that I'll add soon.

Besides this it can be used to 'store' an argument pack and access
its members. In contrast to a `std::tuple<T...>` which is
a container of objects of types `T...` a `TypeList<T...>`
only captures the types themselves . Hence one can easily
create TypeList objects and use them to pass types around
or, e.g., in overload resolution where they can be used for
tag-dispatch.

Notice that adding a template `packer<T...>` doing exactly
the same has been proposed for the standard in [N4115][].
But in my opinion TypeList is a more instructive name.

[N4115]: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4115.html

See merge request !7

Feature/fs1702 cmake add suitesparse support rebased

I had to fix Sphinx and tested it with the LDL branch from dune-istl.
Tested by Tobias and Marco, thanks!

See merge request !8

Thanks Dominic for the hint!