implement auto scaling and translating to fit into final rendering region

[byorgey]

Currently all the tests (e.g. the ones in cairo/test) have to translate and scale the test diagrams manually to get them to show up. In fact what ought to happen is that the final diagram is automatically scaled and translated to fit the chosen image size. Probably the core ought to define some mechanisms for doing this, which individual backends can use as appropriate.

[byorgey]

Starting work on this.