Use demes graphs directly during simulation: (#1101)

* Add ForwardDemesGraph to Python public API
* bump demes to require 0.2.2 in all requirements
  files
* Add extensive new C++-side tests
* ModelParams demography field is now an Optional defaulting to None

    The optional type is:

    typing.Union[fwdpy11.ForwardDemesGraph,
                 fwdpy11.demographic_models.DemographicModelDetails]
* remove unused AmbiguousPulses exception
* Refactor imports of types related to demographic models.
* Remove deprecated API for demographic models
* Remove tests and docs related to removed API

NOTE: this is a rebase of several PR.
The rebase is necessary due to use of
rust depencencies on git.  Such use breaks
any future 'git bisect', so we squash down
to a commit using crates.io versions of all
rust depencencies.

cpp/CMakeLists.txt

@@ -77,13 +77,6 @@ set(EVOLVE_POPULATION_SOURCES evolve_population/init.cc
     evolve_population/no_stopping.cc)
 
 set(DISCRETE_DEMOGRAPHY_SOURCES discrete_demography/init.cc
-    discrete_demography/MigrationMatrix.cc
-    discrete_demography/MassMigration.cc
-    discrete_demography/SetDemeSize.cc
-    discrete_demography/SetExponentialGrowth.cc
-    discrete_demography/SetSelfingRate.cc
-    discrete_demography/SetMigrationRates.cc
-    discrete_demography/DiscreteDemography.cc
     discrete_demography/exceptions.cc)
 
 set (ARRAY_PROXY_SOURCES array_proxies/init.cc)

cpp/demes/forward_graph.cc

@@ -8,6 +8,8 @@ void
 init_forward_graph(py::module &m)
 {
     py::class_<fwdpy11_core::ForwardDemesGraph>(m, "_ForwardDemesGraph")
-        .def(py::init<const std::string & /*yaml*/, std::uint32_t /*burnin*/>(),
-             py::arg("yaml"), py::arg("burnin"), py::kw_only());
+        .def(py::init<const std::string & /*yaml*/, std::uint32_t /*burnin*/,
+                      bool /*round_epoch_sizes*/>(),
+             py::arg("yaml"), py::arg("burnin"), py::arg("round_epoch_sizes"),
+             py::kw_only());
 }