Text metrics in the diagrams backend are now returned correctly.
Moved the cairo specific test stuff to separate file.
The tests on real charts now also run with the diagrams backend.

I split them up so they can be run with either backend.
They are not completely correct yet.
Removed test dependency on cairo backend.

None of the tests has a main function anymore, because of this.
Added fonts that will be included with diagrams backend.
Implemented the default fonts to be used by the diagrams backend.
Fixd some module export issues and implemented that the diagrams backend actually uses its own fonts.
Updated tests with the changes in the diagrams backend. Environment have to be created using IO.
Fixed issue with different font output size in cairo and diagrams.

The metrics in SVG fonts do not seem to match with the definition of the
metrics deliverd by cairo. I now calculate the metrics in the diagrams
backend such that they match the definition of cairo (95%).
Added a test that renders a font using diagrams/cairo and cairo side by side to compare their sizes.
Merge branch 'master' of github.com:timbod7/haskell-chart

Conflicts:
	chart-diagrams/Chart-diagrams.cabal
	chart-diagrams/Graphics/Rendering/Chart/Backend/Diagrams.hs
Fixed compile errors, because of the transition to lens.
Fixed compile error on font compare test due to lens transition.
Updated reference images. Due to the lens transition there are minor hardly recognizable rendering differences.

I have no idea why. I could not spot anything in the pull request that might cause this behaviour.
Added small helper to set all styles back to default.
The backends now correctly set the default styles before rendering.

This was missing before and resulted in different outputs for some tests.
Fixed compile error in the GTK/darcs test case.
Additional documentation of the semantics for backends.
Fixed some dependencies in the tests.
Removed import of Debug.Trace.