Cleaner openmc.deplete namespace with __all__

Provide explicit __all__ lists for files in openmc/deplete
containing classes that should be brought into the "primary"
API. This prevents cluttering the openmc.deplete namespace
caused by the wildcard imports
```
from .nuclide import *
...
```

The abc, cram, and helpers modules are imported simply as
```
from . import abc
from . import cram
from . import helpers
```

openmc/deplete/__init__.py

@@ -35,7 +35,10 @@ from .nuclide import *
 from .chain import *
 from .operator import *
 from .reaction_rates import *
-from .abc import *
+from .atom_number import *
 from .results import *
 from .results_list import *
 from .integrators import *
+from . import abc
+from . import cram
+from . import helpers

openmc/deplete/abc.py

@@ -24,6 +24,13 @@ from .results import Results
 from .chain import Chain
 from .results_list import ResultsList
 
+
+__all__ = [
+    "OperatorResult", "TransportOperator", "ReactionRateHelper",
+    "EnergyHelper", "FissionYieldHelper", "TalliedFissionYieldHelper",
+    "Integrator", "SIIntegrator"]
+
+
 OperatorResult = namedtuple('OperatorResult', ['k', 'rates'])
 OperatorResult.__doc__ = """\
 Result of applying transport operator

openmc/deplete/chain.py

@@ -45,6 +45,8 @@ _REACTIONS = [
 ]
 
 
+__all__ = ["Chain"]
+
 def replace_missing(product, decay_data):
     """Replace missing product with suitable decay daughter.
 

openmc/deplete/cram.py

@@ -13,8 +13,6 @@ import scipy.sparse.linalg as sla
 
 from . import comm
 
-__all__ = ["deplete", "timed_deplete", "CRAM16", "CRAM48"]
-
 
 def deplete(chain, x, rates, dt, matrix_func=None):
     """Deplete materials using given reaction rates for a specified time

openmc/deplete/nuclide.py

@@ -17,6 +17,10 @@ from numpy import empty
 
 from openmc.checkvalue import check_type
 
+__all__ = [
+    "DecayTuple", "ReactionTuple", "Nuclide", "FissionYield",
+    "FissionYieldDistribution"]
+
 
 DecayTuple = namedtuple('DecayTuple', 'type target branching_ratio')
 DecayTuple.__doc__ = """\

openmc/deplete/operator.py

@@ -30,6 +30,9 @@ from .helpers import (
     FissionYieldCutoffHelper, AveragedFissionYieldHelper)
 
 
+__all__ = ["Operator", "OperatorResult"]
+
+
 def _distribute(items):
     """Distribute items across MPI communicator
 

openmc/deplete/reaction_rates.py

@@ -7,6 +7,9 @@ from collections import OrderedDict
 import numpy as np
 
 
+__all__ = ["ReactionRates"]
+
+
 class ReactionRates(np.ndarray):
     """Reaction rates resulting from a transport operator call
 

openmc/deplete/results.py

@@ -16,6 +16,9 @@ from .reaction_rates import ReactionRates
 _VERSION_RESULTS = (1, 0)
 
 
+__all__ = ["Results"]
+
+
 class Results(object):
     """Output of a depletion run
 

openmc/deplete/results_list.py

@@ -5,6 +5,9 @@ from .results import Results, _VERSION_RESULTS
 from openmc.checkvalue import check_filetype_version
 
 
+__all__ = ["ResultsList"]
+
+
 class ResultsList(list):
     """A list of openmc.deplete.Results objects