organizing the docs - put the content in a content folder. put the SimPEG core api docs in core_api

docs/content/api_core/api_FiniteVolume.rst

@@ -0,0 +1,27 @@
+.. _api_FiniteVolume:
+
+Finite Volume
+*************
+
+Any numerical implementation requires the discretization of continuous
+functions into discrete approximations. These approximations are typically
+organized in a mesh, which defines boundaries, locations, and connectivity. Of
+specific interest to geophysical simulations, we require that averaging,
+interpolation and differential operators be defined for any mesh. In SimPEG,
+we have implemented a staggered mimetic finite volume approach (`Hyman and
+Shashkov, 1999 <http://math.lanl.gov/~mac/papers/numerics/HS99B.pdf>`_). This
+approach requires the definitions of variables at either cell-centers, nodes,
+faces, or edges as seen in the figure below.
+
+.. image:: ../../images/finitevolrealestate.png
+   :width: 400 px
+   :alt: FiniteVolume
+   :align: center
+
+
+.. toctree::
+   :maxdepth: 2
+
+   api_Mesh
+   api_DiffOps
+   api_InnerProducts