requires an upstream fix

Feature/cache quadrature information 2

Supersedes !53

See merge request !54

Reimplement temporary declaration

We previously completely avoided loopy for temporary declaration.
We now rely on it again, but have DuneTemporaryVariable, which is
capable of doing a bit more things (and at the same time handles
the indexing question)

This is finished and tests are passing, I will remove the WIP flag once a necessary upstream change is in master.

See merge request !52

This removes:
- The now obsolete quadrature_loop_statement.
- Quadrature weights are now a globalarg and we do not create a
temporary anymore.

We previously completely avoided loopy for temporary declaration.
We now rely on it again, but have DuneTemporaryVariable, which is
capable of doing a bit more things (and at the same time handles
the indexing question)

Quadrature loop for sum factorization



See merge request !50

[Fix] Make pytest pass



See merge request !49

Feature/next sumfac

Next generation towards sum factorization
* fixes #49 by introducing an interface class between visitor and generator functions

See merge request !48

In sum factorization we will have different temporary shape and access.

and use it as the only sumfact test until it works.

* Enable backend functions which are *not* generators
* Use the sumfac switch as a default switch

The backend selecting mechanism needs all modules to be imported.
This commit restructures the package to be able to do that. Placement
of some functions felt weird, but this can still be changed.
No more placements in __init__.py anymore though, as this will
result in cyclic dependencies.

Sum factorization!

This is the new merge requests that supersedes both !42 and !45.

Also bumps submodules in various places, as loopy has had a rough week.

Also fixes #47, #20 .

See merge request !47