Integrator and Callback Interfaces, Composite Algorithm

For more details on this release, see the post here: http://juliadiffeq.org/2017/01/08/base.html . Lots of the docs are already updated / are updating. Tests won't pass until ParameterizedFunctions and DiffEqDevTools tags go though, but version requirements should ensure there's no breakage. This should be compatible with the previous DiffEqBase version as well (just not the tests).