Added dynamic class/function/method dispatch. All tests pass.
cpp_standalone is simplified.
Rolled back dynamic switching, added device_override instead, made build
always imported
Add function signatures as the first line of the docstring for functions with `@device_override` -- otherwise the signatures are not correctly displayed in the docs
Merge pull request #199 from brian-team/dynamic_device

Dynamic class/function/method dispatch. Closes #184