File names, import issues

[adamgayoso]

1. File (module) names should be all lowercase see: https://www.python.org/dev/peps/pep-0008/#package-and-module-names -- and this is causing an issue with autosummary for nice class pages in the docs
2. For an import like this

   Cassiopeia/cassiopeia/data/CassiopeiaTree.py

   Line 27 in 4a4ba1a

   from cassiopeia.data import utilities

   utilities should be a subpackage in that directory.
3. I would avoid cross package imports like this

   Cassiopeia/cassiopeia/data/CassiopeiaTree.py

   Line 34 in 4a4ba1a

   from cassiopeia.solver import solver_utilities

   as I believe some parts of solver depend on the tree
4. For an import like this

   Cassiopeia/cassiopeia/solver/NeighborJoiningSolver.py

   Lines 16 to 20 in 4a4ba1a

   	from cassiopeia.solver import (
   	DistanceSolver,
   	dissimilarity_functions,
   	solver_utilities,
   	)

   I feel it gets kind of weird because solver_utilities is a file in solver but the other two are imported into that namespace via the init file.
5. Imports like the first and third here

   Cassiopeia/cassiopeia/simulator/CompleteBinarySimulator.py

   Lines 11 to 13 in 4a4ba1a

   	from cassiopeia.data.CassiopeiaTree import CassiopeiaTree
   	from cassiopeia.mixins import TreeSimulatorError
   	from cassiopeia.simulator.TreeSimulator import TreeSimulator

   should not have the file name in them, as these are imported via the init of that directory
6. I would rename the github repo to cassiopeia to remove the capital C so that the name reflects the python package name. All old urls will work still.